Surface-emission laser diode operable in the wavelength band of 1.1-7mum and optical telecommunication system using such a laser diode

ABSTRACT

A surface-emission laser diode includes a distributed Bragg reflector tuned to wavelength of 1.1 μm or longer, wherein the distributed Bragg reflector includes an alternate repetition of a low-refractive index layer and a high-refractive index layer, with a heterospike buffer layer having an intermediate refractive index interposed therebetween with a thickness in the range of 5-50 nm.

BACKGROUND OF THE INVENTION

[0001] This invention generally relates to laser diodes and further tothe art of optical telecommunication that uses a laser diode. Especiallythis invention is related to a so-called surface-emission laser diodethat emits a laser beam in a generally vertical direction to a substratesurface. Also, the present invention is related to an opticaltransmission/reception system and optical-fiber telecommunication systemthat uses such a surface-emission laser diode.

[0002] A surface-emission laser diode is a laser diode that emits alaser beam in a generally vertical direction from a surface of asubstrate. By using surface-emission laser diodes, two-dimensional arrayintegration of laser diode is achieved easily. Further, the laser diodehas an advantageous feature of relatively narrow divergent angle of theoutput optical beam (about 10 degrees), which is particularly suitablefor coupling with optical fibers. Furthermore, inspection of the laserdiode device is made easily in a surface-emission laser diode.

[0003] Thus, surface-emission laser diodes are suited to construct anoptical transmission module (optical interconnection apparatus) ofparallel-transmission type, and research and development are conductedprosperously. The immediate application of the optical interconnectionapparatus would be the parallel connection between computers or circuitboards in a computer, including short-range optical-fibertelecommunication. In future, application to a large-scale computernetwork and trunk line system of long-range, large-capacitytelecommunication is expected.

[0004] Generally, a surface-emission laser diode includes an activelayer of a group III-V semiconductor material such as GaAs or GaInAs,and an optical resonator is formed by disposing an upper semiconductorBragg reflector and a lower semiconductor Bragg reflector arrangedrespectively above and below the active layer.

[0005] In such a construction, the length of the optical resonator isremarkably short as compared with the case of an edge-emission laserdiode. Therefore, it is necessary to increase the reflectance of thereflector to a high value (99% or more) for facilitating laseroscillation. Because of this, it is practiced to use a semiconductorBragg reflector in a surface-emission laser diode as a reflector,wherein a semiconductor Bragg reflector is formed of an alternate andrepetitive stacking of a high-refractive index material such as GaAs anda low refractive index material such as GaAs with a period of 1/4wavelength.

[0006] However, in the conventional semiconductor Bragg reflector thathas the structure mentioned above, there arises a spike structure in theenergy band as a result of band discontinuity at the hetero interface,at which the materials of different bandgaps are jointed, and the spikestructure thus formed tends to function as a barrier against carriers.Thereby, there arises a problem in that the semiconductor multilayerpart increases the resistance of the laser diode. Because of this,conventional surface-emission laser diodes constructed on a GaAssubstrate have suffered from the problem of comparatively high operatingvoltage of about 2.5 volts or more. Because of this, it has beendifficult to use the surface-emission laser diode with a CMOS driverintegrated circuit, which produces a laser driving voltage of 2 volts atbest. The itemization of this operating voltage of 2.5 volts is: 1.5Vfor the diode part; and 1V for the device resistance. In order to reducethe operational voltage below 2 V, it is necessary to reduce the deviceresistance by one-half, while it is extremely difficult to meet for thisrequirement at the present stage of technology.

[0007] In the case of a laser diode of long-wavelength band for use inoptical telecommunication, such as the laser diode of 1.3 μm band or1.55 μm, a low voltage operation is expected in view of the fact thatonly a voltage of 1 volt or less is applied to the diode part of thelaser diode. Unfortunately, the desired low voltage operation is notmaterialized in such a long wavelength laser diode. In conventionallong-wavelength laser diode, InP is used for the substrate and InGaAsPis used for the active layer. In such a system, the lattice constant ofInP constituting the substrate is large, and it is difficult to achievea large refractive-index difference in the reflector when a materialthat achieves lattice matching with the InP substrate is used for thereflector. Consequently, it has been necessary to stack 40 or more pairsin the reflector for realizing sufficient reflectance. In such aconstruction, however, the resistance of the reflector increases againas a result of increased stacking number of the reflector. Thus, it hasbeen difficult to drive the laser diode driver by a CMOS integratedcircuit.

[0008] In a surface-emission laser diode formed on an InP substrate,there is another problem of change of laser characteristic caused by thetemperature. Because of this, it has been necessary to add an apparatusfor stabilizing the temperature in the laser diode constructed on suchan InP substrate. However, the use of such a temperature regulator isdifficult in the apparatus for home use, which is subjected to a severedemand of cost reduction. Because of these problems of increased numberof stacking in the reflector and the poor temperature characteristics,practical long-wavelength surface-emission laser diode has not yetcommercialized.

[0009] In order to deal with the foregoing problems, there is a proposalto construct a surface-emission laser diode on a GaAs substrate by usingan AlInP layer, which achieves a lattice matching with the GaAssubstrate, in at least one of the upper and lower semiconductor Braggreflectors as the low refractive index layer, and further by using aGaInNAs layer in at least one of the upper and lower semiconductor Braggreflectors, as disclosed in Japanese Laid-Open Patent Application9-237942, such that a large refractive index difference is realized inthe reflector and the number of stacking therein is reduced whilemaintaining high reflectance.

[0010] In the foregoing conventional art, the bandgap of the activelayer is reduced by 1.4 eV by using GaInNAs, in which N is introducedinto the III-group V semiconductor material system of GaInAs. As aresult, the laser diode can produce an optical beam with a wavelengthlonger than 0.85 ìm. In the aforementioned prior art, it should be notedthat the material system of GaInNAs can achieve a lattice matching withthe GaAs substrate. Further, the prior art describes the semiconductorlayer of GaInNAs can be a promising material for the long-wavelengthsurface-emission laser diode operable in the 1.3 micron band and 1.55micron band.

[0011] In spite of such a description in the prior art with regard tothe possibility of surface emission laser diode operable in thewavelength band longer than 0.85 μm, there has no such a laser diodeactually materialized. The present situation would be something likethat the theoretical construction is already established but the actualconstruction for materializing the laser diode is not discovered yet.

[0012] In one example, there is a laser diode that uses a semiconductorBragg reflector formed by stacking high-refractive index material layersof GaAs and low refractive index material layers of AlAs alternately asnoted above with the periods of 1/4 wavelength. However, the laser diodestructure thus formed does not provide optical emission at all, oroperates but only with low power, indicating that the efficiency ofoptical emission is extremely small.

[0013] Similarly, there is a laser diode disclosed in the Japanese LaidOpen Patent Application 9-237942 in which an AlInP layer is used for thelow refractive index layer of the semiconductor Bragg reflector. In thiscase, too, the luminous efficacy of the laser diode is far from thelevel of practical use.

[0014] The reason of this unsatisfactory result is attributed to thechemical activity of the material including Al. More specifically, it isthought that the use of a material containing Al easily invitesformation of crystal defects originating from Al. Thus, there have beenproposals, as in the Japanese Laid-Open Patent Application 8-340146 andJapanese Laid-Open Patent Application 7-307525, to construct thesemiconductor Bragg reflector with materials free from Al such as GaInNPand GaAs. However, the material system of GaInNP and GaAs can provide arefractive-index difference of about half as compared with the materialsystem of AlAs and GaAs. Thus, the stacking number in the reflector hasto be increased, and the object of reducing the resistance of thesurface-emission laser diode is not attained.

[0015] Thus, at present, the surface-emission laser diode operable atthe long-wavelength of 1.1-1.7 ìm does not exist, and because of this,it is not possible to construct a computer network or optical-fibertelecommunication system that uses such a laser diode.

[0016] As explained before, in a conventional surface-emission laserdiode, it was also not possible to use a CMOS circuit for the laserdiode driver, and it has been necessary to use an expensive specialdriver circuit. On the other hand, if a mass-produced CMOS driverintegrated circuit could be used, the cost of the opticaltelecommunication system that uses such a surface-emission laser diodewould be reduced significantly.

[0017] Furthermore the use of a CMOS circuit can reduce the power supplyvoltage of the driver integrated circuit as well from 5V to 3.3V. Withthis, it is possible to reduce the power consumption of the system toabout one-half, and a very large effect of electric power saving isobtained.

[0018] As noted before, there is a widespread expectation ofoptical-fiber telecommunication in relation to computer networks, andthe like. Especially, there is a need of realizing a low cost system inorder that the public accepts such an optical telecommunication system.Unfortunately, the surface-emission laser diode that can be used for.this purpose and can be used with a low-cost CMOS driver integratedcircuit, and oscillates at the long-wavelength band of 1.1-1.7 ìm doesnot exist. Hence, the telecommunication system that uses such a surfaceemission laser diode does not exist.

[0019] Meanwhile, in the above-mentioned semiconductor Bragg reflector,in which semiconductor layers of different bandgaps are grownalternately, there arises the problem of spike formation in the bandstructure thereof at the hetero interface as a result of the banddiscontinuity. When such a spike structure is formed, the spikestructure functions as a barrier with regard to the carriers. Thus,there arises a problem in that the electric resistance becomes very highin the semiconductor multilayer part of the surface-emission laserdiode. This effect also contributes to the large drive voltage of 2.5 Vfor the surface-emission laser diode constructed on a GaAs substrate. Asnoted previously, it has been difficult to drive a laser diode havingsuch a large driving voltage by the driver integrated circuit formed ofa CMOS circuit (driving voltage is below 2 volts).

[0020] As noted previously, the itemization of this operating voltage of2.5 volts is: 1.5V for the diode part; and 1V for the device resistance,and it is necessary to reduce the device resistance by one-half in orderto drive the laser diode with a drive voltage below 2 volts. However,this is a very difficult subject.

[0021] Recently, the optical systems are used also for peripheraltransmission/reception systems, and there is a widespread expectationabout the computer networks using the optical-fiber telecommunicationtechnology including such a peripheral transmission/reception system.Especially, there is a keen interest about a low cost optical systemrequired for spreading of the optical fiber technology to the generalpublic. However, the surface-emission laser diode that can be used forthis purpose and can be used with a low-cost CMOS driver integratedcircuit, and oscillates at the long-wavelength band of 1.1-1.7 ìm doesnot exist yet. Hence, the telecommunication system that uses such asurface emission laser diode does not exist at the moment.

[0022] In such an optical-fiber telecommunication system that uses thelong-wavelength surface-emission laser diode operating at the wavelengthband of 1.1-1.7 ìm, the photodetection device constructed on a Sisubstrate cannot be used, as such a photodetection device cannot detectthe wavelength of 1.1-1.7 ìm. In such a system, it is necessary to use aphotodetection device that has a sensitivity to the wavelength of1.1-1.7 ìm. However, the photodetection device that has sensitivity tothe desired wavelength band of 1.1-1.7 ìm is expensive as compared withthe low cost Si photodetection device. Thus, simple replacement of aconventional Si photodetection device with the photodetection devicehaving the sensitivity to the wavelength of 1.1-1.7 ìm causes anincrease of cost of the whole optical-fiber telecommunication systemThus, in order to realize an optical telecommunication system that usesthe long-wavelength surface-emission laser diode of 1.1-1.7 ìm band, anapproach other than replacing the conventional Si photodetection devicewith an expensive photodetection device is needed.

[0023] Furthermore, a GaInNAs active layer having a high strain is usedin the long-wavelength surface-emission laser diode, as will beexplained below. In such a laser diode, deterioration of devicecharacteristic may be caused as a result of the thermal stress caused bythe difference of linear thermal expansion coefficient with regard tothe mounting substrate.

[0024] Meanwhile, in the optical-fiber telecommunication system thatuses a surface-emission laser diode, it is possible to arrange a numberof laser diode elements, each formed of a surface-emission laser diode,with high integration density. Thus, the distance between the opticalfibers can be reduced as compared with the case in which a conventionaledge-emission laser diode is used for the laser diode array. Generally,optical fibers accommodated in an optical cable is provided with amarker band or a plastic ring in the form of a coloring layer oridentification code (ID mark), in order to allow identification of thetransmission line. When the distance between the optical fibers isreduced, the space available for these protection layers or rings isreduced.

[0025] In the production of an optical module that accommodates thereinan array of surface-emission laser diodes, it should be noted that theproduced optical module would becomes a defective product unless anecessary quality is secured for a predetermined number of laser diodeelements in the array. Otherwise, the product loses the value thereof.

[0026] This issue is related to the yield of the laser diode productionprocess. In the production of the module product that uses an arrayarrangement of the laser diode elements, there is an acute demand ofestablishing the production process in which the modules that functionnormally are utilized efficiently and the yield of production of themodule is improved.

[0027] Summarizing above, there is no available long-wavelengthsurface-emission laser diode operable at the wavelength band of 1.1-1.7ìm and that there is no available optical transmission/reception systemthat uses such a laser diode.

SUMMARY OF THE INVENTION

[0028] Accordingly, it is a general object of the present invention toprovide a novel and useful surface-emission laser diode operable in along wavelength band and an optical transmission/reception system oroptical telecommunication system that uses such a surface-emission laserdiode.

[0029] Another and more specific object of the present invention is toprovide a surface-emission laser diode or laser diode array having adistributed Bragg reflector tuned to a wavelength of 1.1 μm or longerwherein the electric resistance of the distributed Bragg reflector isminimized while maintaining high reflectance.

[0030] Another object of the present invention is to provide asurface-emission laser diode or laser diode array in which anintermediate layer is interposed between a high refractive index layerand a low refractive index layer constituting a distributed Braggreflector with a refractive index intermediate between the highrefractive index layer and the low refractive index layer, wherein thethickness of the intermediate layer is optimized for minimizing theresistance of the distributed Bragg reflector while maintaining a highreflectance.

[0031] Another object of the present invention is to provide asurface-emission laser diode or laser diode array in which anintermediate layer or heterospike buffer layer is interposed between alow refractive index layer having a wide bandgap and a high refractiveindex layer having a narrow bandgap with an intermediate bandgap,wherein the compositional profile of Al in the heterospike buffer layeris optimized so as to minimize the resistance of the distributed Braggreflector while maintaining a high reflectance.

[0032] Another object of the present invention is to provide an opticalinterconnection system or optical telecommunication system using such asurface-emission laser diode or surface-emission laser diode array.

[0033] Another object of the present invention is to provide an opticaltransmission/reception system that uses a long-wavelengthsurface-emission laser diode operable at the laser oscillationwavelength of 1.1-1.7 ìm with low operating voltage and smalloscillation threshold current.

[0034] Another object of the present invention is to provide an opticaltransmission/reception system suitable for construction inside abuilding by using a surface-emission laser diode chip in which theoperating voltage is reduced and the threshold current for laseroscillation is reduced.

[0035] Another object of the present invention is to provide astabilized optical transmission/reception system by using along-wavelength surface-emission laser diode chip operating stably atthe wavelength of 1.1-1.7 ìm for the optical source.

[0036] Another object of the present invention is to eliminate variousproblems that arise when such an optical transmission/reception systemis actually incorporated in an electronic apparatus.

[0037] Another object of the present invention is to provide a low-costand energy-saving optical transmission/reception system by using asurface-emission laser diode chip operable at low voltage with a smallthreshold current of laser oscillation.

[0038] Another object of the present invention is to facilitate theconstruction of an optical-fiber telecommunication system that uses asurface-emission laser diode operating at low voltage with lowoscillation threshold current as an optical source, by increasing thelength of the optical fiber cable extending from a module package beyonda certain length, and hence by improving the productivity of assemblingthe module package.

[0039] Another object of the present invention is to provide anoptical-fiber telecommunication system that enables optical transmissionof large capacity with low cost, by using a surface-emission laser diodehaving a reduced operational voltage and reduced oscillation threshold,as an optical source.

[0040] Another object of the present invention is to provide a reliableoptical-fiber telecommunication system by using a surface-emission laserdiode having a low operational voltage and low oscillation threshold asan optical source, such that the change of operational characteristic ofthe laser diode is suppressed and the lifetime of the laser diode isincreased.

[0041] Another object of the present invention is to provide an opticaltelecommunication system realizing excellent optical coupling between alaser diode and an optical fiber, by using a surface-emission laserdiode operable at a low operational voltage with low oscillationthreshold, for an optical source.

[0042] Another object of the present invention is to provide an opticaltelecommunication system having a simple construction characterized byreduced number of parts and is simultaneously capable of realizingexcellent optical coupling as a result of use of a surface-emissionlaser diode operable at a low operational voltage with low oscillationthreshold, for an optical source.

[0043] Another object of the present invention is to provide an opticaltelecommunication system realizing excellent optical coupling between alaser diode and an optical fiber, by using a surface-emission laserdiode operable at a low operational voltage with low oscillationthreshold, for an optical source.

[0044] Another object of the present invention is to provide an opticaltelecommunication system capable of using a laser diode without causingdamage therein, by using a surface-emission laser diode operable at alow voltage with low threshold current of laser oscillation.

[0045] According to the present invention, the surface-emission laserdiode oscillates at the wavelength band of 1.1-1.7 microns suitable foruse in an optical-fiber telecommunications in computer networks orlong-range, large-capacity telecommunication trunks. Thesurface-emission laser diode of the present invention oscillates stablyat this wavelength band with low operating voltage and low oscillationthreshold. Conventionally, such a low surface-emission laser diode didnot exist. The laser of the present invention oscillates at theaforementioned wavelength region with low operational voltage and lowthreshold current as a result of use of an improved semiconductor Braggreflector. As a result of low power consumption, the surface-emissionlaser diode of the present invention successfully eliminates the heatingproblem. Thereby, the surface-emission laser diode of the presentinvention oscillates stably. By using such a surface-emission laserdiode, it became possible to construct a practical point-to-pointoptical transmission/reception system with low cost.

[0046] In constructing such a point-to-point opticaltransmission/reception system, the present invention avoids localizedbending of the transmission path. As a result, the opticaltransmission/reception system connects two points easily and with lowcost, without damaging the optical fiber.

BRIEF DESCRIPTION OF THE DRAWINGS

[0047]FIG. 1 is a diagram showing a cross-sectional view of along-wavelength surface-emission laser diode according to a firstembodiment of this invention;

[0048]FIG. 2 is a diagram showing an example of reflection spectrum of adistributed Bragg reflector used in the laser diode of FIG. 1;

[0049]FIG. 3 is a cross-sectional view showing the constitution of asemiconductor Bragg reflector used in the long-wavelengthsurface-emission laser diode of the first embodiment;

[0050]FIG. 4 is a diagram showing a compositional gradation of aheterospike buffer layer used in the semiconductor Bragg reflectorconstituting a part of the laser diode of the first embodiment;

[0051]FIG. 5 is a diagram showing an example of changing an Alcomposition in the heterospike buffer layer;

[0052]FIG. 6 is a diagram showing a result of evaluating adifferentiation sheet resistance of the heterospike buffer layer of FIG.4;

[0053]FIG. 7 is a diagram showing the band structure of a distributedBragg reflector near a heterojunction interface in a thermal equilibriumstate;

[0054]FIG. 8 is a diagram showing the band structure of the heterospikebuffer layer of FIG. 3 in a thermal equilibrium state;

[0055]FIG. 9 is a diagram showing an example of the band structure ofthe heterospike buffer layer used in the present invention;

[0056]FIG. 10 is a diagram showing an example of the band structure ofthe heterospike buffer layer used in the present invention;

[0057]FIG. 11 is a diagram showing an example of the band structure ofthe heterospike buffer layer used in the present invention;

[0058]FIG. 12 is a diagram showing an example of the band structure ofthe heterospike buffer layer used in the present invention;

[0059]FIG. 13 is a diagram showing the relationship between thedifferential sheet resistance of the distributed Bragg reflector and theAl compositional profile in the heterospike buffer layer;

[0060]FIG. 14 is another diagram showing the relationship between thedifferential sheet resistance of the distributed Bragg reflector and theAl compositional profile in the heterospike buffer layer;

[0061]FIG. 15 is a diagram showing another band structure of theheterospike buffer layer;

[0062]FIG. 16 is a diagram showing the relationship between thereflectance of the distributed Bragg reflector and the thickness of theheterospike buffer layer;

[0063]FIG. 17 is a diagram showing the relationship between theresistance of the distributed Bragg reflector and the thickness of theheterospike buffer layer;

[0064]FIG. 18 is another diagram showing the relationship between theresistivity of the distributed Bragg reflector and the thickness of theheterospike buffer layer;

[0065]FIG. 19 is a further diagram showing the relationship between theresistivity of the distributed Bragg reflector and the thickness of theheterospike buffer layer;

[0066]FIG. 20 is a further diagram showing another example of the bandstructure of the heterospike buffer layer;

[0067]FIG. 21 is a diagram showing the relationship between theresistivity of the distributed Bragg reflector having the heterospikebuffer layer of FIG. 20 and the thickness of the heterospike bufferlayer;

[0068]FIG. 22 is another diagram showing the relationship between theresistivity of the distributed Bragg reflector having the heterospikebuffer layer of FIG. 20 and the thickness of the heterospike bufferlayer;

[0069]FIG. 23 is a diagram showing the relationship between theresistance of various distributed Bragg reflectors and the-thickness ofthe heterospike buffer layer;

[0070]FIG. 24 is another diagram showing the relationship of theresistance of various distributed Bragg reflectors and the thickness ofthe heterospike buffer layer;

[0071]FIG. 25 is a diagram showing the relationship between thereflectance of various distributed Bragg reflectors and the thickness ofthe heterospike buffer layer;

[0072]FIG. 26 is another diagram showing the relationship between thereflectance of various distributed Bragg reflectors and the thickness ofthe heterospike buffer layer;

[0073]FIG. 27 is a sectional view showing the constitution of thelong-wavelength surface-emission laser diode according to a secondembodiment of the present invention;

[0074]FIG. 28 is a diagram showing a room temperature photoluminescencespectrum of the active layer formed of a GaInNAs/G s double quantum wellstructure;

[0075]FIG. 29 is a diagram showing a sample structure;

[0076]FIG. 30 is a diagram showing a depth profile of nitrogen andoxygen;

[0077]FIG. 31 is a diagram snowing a depth profile of Al;

[0078]FIG. 32 is a diagram showing the structure obtained for a case inwhich growth interruption process is used in the form of a carrier gaspurging process;

[0079]FIG. 33 is a diagram showing a depth profile of the Al for thecase in which a growth interruption process is provided and purging isconducted by using a hydrogen gas;

[0080]FIG. 34 is a diagram showing a depth profile of nitrogen andoxygen for the case in which a growth interruption process is providedand purging is made with a hydrogen gas;

[0081]FIG. 35 is a plane view showing a wafer and a laser diode chipin-which the long-wavelength surface-emission laser diode of thisinvention is formed;

[0082]FIG. 36 is a diagram showing an example of opticaltransmission/reception system that connects an optical source and aphotodetection unit by a straight the transmission path;

[0083]FIG. 37 is a diagram showing an overall view of the above opticaltransmission/reception system;

[0084]FIG. 38 is a diagram showing an example of bending thetransmission path connecting an optical source and a photodetection unitat a right angle for avoiding an obstacle;

[0085]FIG. 39 is a diagram showing an example of the opticaltransmission/reception system of this invention that avoids an obstacleby bending the transmission path between an optical source and aphotodetection unit;

[0086]FIG. 40 is a diagram showing another example of opticaltransmission/reception system of this invention that avoids an obstaclebetween the optical source and the photodetection unit by bending thetransmission path;

[0087]FIG. 41 is a diagram showing an example of an opticaltransmission/reception system that uses a long-wavelengthsurface-emission laser diode of this invention as the optical source;

[0088]FIG. 42 is a plane view showing an example of a room in which theoptical transmission/reception system of this invention is provided;

[0089]FIG. 43 is a plane view showing an example of a room in which aconventional optical transmission/reception system is provided;

[0090]FIG. 44 is a plane view showing a further example of a room inwhich a conventional optical transmission/reception system is provided;

[0091]FIG. 45 is a schematic diagram showing an example of the opticaltransmission/reception system of this invention;

[0092]FIG. 46 is a schematic diagram showing another example of theoptical transmission/reception system of this invention;

[0093]FIG. 47 is a diagram showing an example of the electrophotographiccopying machine to which the present invention is applied;

[0094]FIG. 48 is a diagram showing an example of an electrophotographycopying machine that uses an optical transmission/reception system ofthis invention;

[0095]FIG. 49 is a diagram showing an example of an ink jet recordapparatus to which the present invention is applied;

[0096]FIG. 50 is a diagram showing an example of the ink jet recordapparatus that includes an optical transmission/reception system of thisinvention;

[0097]FIG. 51 is a diagram showing further example of the opticaltransmission/reception system of the present invention;

[0098]FIG. 52 is a diagram showing an example of optical-fibertelecommunication system to which a long-wavelength surface-emissiondiode according to an embodiment of this invention is connected;

[0099]FIG. 53 is a diagram showing a bi-directional system constructedby using the long-wavelength surface-emission laser diode of anembodiment and an optical-fiber telecommunication system connectedthereto;

[0100]FIG. 54 is a diagram showing an example of large capacityoptical-fiber telecommunication system that uses plural optical fibergroups in which the long-wavelength surface-emission laser diode of thisinvention is used;

[0101]FIG. 55 is a diagram showing a long-wavelength surface-emissionlaser diode and an optical-fiber telecommunication system connectedthereto according to an embodiment of this invention;

[0102]FIG. 56 is a diagram showing the constitution of an opticalconnection module used in an optical-fiber telecommunication systemtogether with the a -wavelength surface-emission laser diode accordingto an embodiment of this invention;

[0103]FIG. 57 is another diagram showing the constitution of an opticalconnection module used in an optical-fiber telecommunication systemtogether with a long-wavelength surface-emission laser diode accordingto an embodiment of this invention;

[0104]FIG. 58 is a diagram showing another constitution of anoptical-fiber telecommunication system that uses a long-wavelengthsurface-emission laser diode according to an embodiment of thisinvention;

[0105]FIG. 59 is a diagram showing the constitution of anotheroptical-fiber telecommunication system that uses a long-wavelengthsurface-emission laser diode according to an embodiment of thisinvention;

[0106]FIG. 60 is a diagram explaining the constitution of an opticalconnection module used in an optical-fiber telecommunication systemtogether with a long-wavelength surface-emission laser diode accordingto an embodiment of this invention;

[0107]FIG. 61 is a diagram showing the constitution of an optical-fibertelecommunication system that uses a long-wavelength surface-emissionlaser diode according to an embodiment of this invention;

[0108]FIG. 62 is a diagram showing length setting of optical fiber forguiding in an optical-fiber telecommunication system that uses along-wavelength surface-emission laser diode according to a firstembodiment of this invention;

[0109]FIG. 63 is a diagram showing the constitution of an optical-fibertelecommunication system that uses a long-wavelength surface-emissionlaser diode and plural optical fibers according to an embodiment of thisinvention;

[0110]FIG. 64 is a diagram showing an emission angle of an optical beamemitted from a long-wavelength surface-emission laser diode according toan embodiment of the present invention;

[0111] FIGS. 65A-65C are diagrams showing the process of fixing pluraloptical fibers with a resin according to an embodiment of thisinvention;

[0112] FIGS. 66A-66C are diagrams showing a the connect mode of along-wavelength surface-emission laser diode to plural optical fibersaccording to an embodiment of this invention;

[0113]FIG. 67 is a diagram showing possible locations of optical fibersin a closely packed state according to an embodiment of this invention;

[0114]FIG. 68 is a diagram showing an example of arranging pluraloptical fibers with a closest packed state according to an embodiment ofthis invention;

[0115]FIG. 69 is a cross-sectional view showing the constitution of anoptical fiber connected to a long-wavelength surface-emission laserdiode according to an embodiment of this invention;

[0116]FIG. 70 is a plane view showing the constitution of theoptical-fiber telecommunication system that uses a long-wavelengthsurface-emission laser diode and an optical fiber connected theretoaccording to an embodiment of this invention;

[0117]FIG. 71 is plane view showing the constitution of a bi-directionaloptical-fiber telecommunication system that uses a long-wavelengthsurface-emission laser diode and an optical fiber connected theretoaccording to an embodiment of this invention;

[0118]FIG. 72 is a plane view showing the constitution of LAN in abuilding in which the function of a long-wavelength surface-emissionlaser diode and the function of an optical fiber connected thereto areseparated;

[0119]FIGS. 73A and 73B are respectively a plan view showing along-wavelength surface-emission laser diode and an integral opticalfiber telecommunication apparatus and a cross-sectional view of anoptical waveguide according to an embodiment of this invention;

[0120]FIGS. 74A and 74B are diagrams showing the constitution of along-wavelength surface-emission laser diode chip according to anembodiment of this invention;

[0121]FIG. 75 is a diagram explaining the operation of a semiconductorlaser diode chip of FIGS. 74A and 74B;

[0122]FIGS. 76A and 76B are diagrams showing the constitution of along-wavelength surface-emission laser diode chip according to anembodiment of this invention;

[0123]FIG. 77 is a diagram explaining the operation of a laser diodechip shown in FIGS. 59A and 59B;

[0124]FIG. 78 is a diagram showing an optical transmission part of atelecommunication system in which the long-wavelength surface-emissionlaser diode according to an embodiment of this invention is used;

[0125]FIG. 79 is a diagram showing an optical transmission part of atelecommunication system in which the long-wavelength surface-emissionlaser diode of an embodiment of this invention is used;

[0126]FIG. 80 is a cross-sectional view showing an optical couplingdevice used in a long-wavelength surface-emission laser diode accordingto an embodiment of this invention;

[0127]FIG. 81 is a cross-sectional view showing the optical couplingdevice of FIG. 63;

[0128]FIG. 82 is a cross-sectional view showing an optical couplingdevice that couples with a long-wavelength surface-emission laser diodeaccording to an embodiment of this invention;

[0129]FIG. 83 is a cross-sectional view showing an optical couplingdevice that couples optically with a long-wavelength surface-emissionlaser diode according to an embodiment of this invention;

[0130]FIG. 84 is a cross-sectional view showing an optical fiberfixation apparatus used with a long-wavelength surface-emission laserdiode according to an embodiment of this invention;

[0131]FIG. 85 is a cross-sectional view showing the structure of anoptical coupling device;

[0132]FIG. 86 is a diagram showing a positional relationship between amonitor photodetection device and a surface-emission laser diode in anoptical-fiber telecommunication system that uses the long-wavelengthsurface-emission laser diode according to an embodiment of thisinvention;

[0133]FIG. 87 is a block diagram showing the constitution of a controlcircuit that controls output of a surface-emission laser diode accordingto an embodiment of this invention;

[0134]FIG. 88 is a diagram showing the constitution of an optical-fibertelecommunication system that uses a long-wavelength surface-emissionlaser diode according to an embodiment of this invention;

[0135]FIG. 89 is a schematic diagram showing the constitution of anoptical-fiber telecommunication system that uses a long-wavelengthsurface-emission laser diode according to an embodiment of thisinvention;

[0136]FIG. 90 is a diagram showing a monitor photodetection device, areflection surface and a surface-emission laser diode of anoptical-fiber telecommunication system that uses the long-wavelengthsurface-emission laser diode according to an embodiment of thisinvention;

[0137]FIG. 91 is a diagram showing then constitution of an optical-fibertelecommunication system formed of a long-wavelength surface-emissionlaser diode, an optical fiber and an optical connector according to anembodiment of this invention;

[0138]FIG. 92 is a diagram showing the positional relationship betweenan optical fiber, a ferule and divided sleeves according to anembodiment of this invention;

[0139]FIG. 93 is a diagram showing the relationship between a lightemission angle and beam diameter in a long-wavelength surface-emissionlaser diode according to an embodiment of this invention;

[0140]FIG. 94 is a diagram showing the relationship between beamspreading and a core diameter and an optical path length of along-wavelength surface-emission laser diode according to an embodimentof this invention;

[0141]FIG. 95 is a diagram showing a calculation example of arelationship between a beam diameter and an optical path length of along-wavelength surface-emission laser diode according to an embodimentof this invention;

[0142]FIG. 96 is a diagram showing the constitution of a connection partof a laser diode and an optical fiber of an optical-fibertelecommunication system that uses a long-wavelength surface-emissionlaser diode according to an embodiment of this invention;

[0143]FIGS. 97A and 97B are diagrams showing the constitution of aconnection part of a laser diode and an optical waveguide of anoptical-fiber telecommunication system that uses a long-wavelengthsurface-emission laser diode according to an embodiment of thisinvention;

[0144]FIG. 98 is a diagram showing the constitution of a connection partof a laser diode and an optical waveguide in an optical-fibertelecommunication system that uses a long-wavelength surface-emissionlaser diode according to an embodiment of this invention;

[0145]FIG. 99 is a diagram showing the constitution of an optical-fibertelecommunication system that uses a long-wavelength surface-emissionlaser diode of an embodiment of this invention in which the laser diodeand the optical fiber are coupled directly;

[0146]FIG. 100 is a diagram showing the constitution of an optical-fibertelecommunication system that uses a long-wavelength surface-emissionlaser diode according to an embodiment of this invention;

[0147]FIG. 101 is a diagram showing the constitution of an optical-fibertelecommunication system that uses a long-wavelength surface-emissionlaser diode according to an embodiment of this invention;

[0148]FIG. 102 is a diagram showing the constitution of an optical-fibertelecommunication system that uses a long-wavelength surface-emissionlaser diode according to an embodiment of this invention;

[0149]FIG. 103 is a diagram showing the constitution of an optical-fibertelecommunication system that uses a long-wavelength surface-emissionlaser diode according to an embodiment of this invention;

[0150]FIGS. 104A and 104B are diagrams showing an example of mounting along-wavelength surface-emission laser diode of an embodiment of thisinvention;

[0151]FIG. 105 is a diagram showing the constitution of an optical-fibertelecommunication system that uses a long-wavelength surface-emissionlaser diode according to an embodiment of this invention;

[0152]FIG. 106 is a block diagram showing the constitution of a controldevice used with an optical-fiber telecommunication system according toan embodiment of this invention in which a long-wavelengthsurface-emission laser diode is used;

[0153]FIG. 107 is a diagram showing the constitution of an optical-fibertelecommunication system that uses a long-wavelength surface-emissionlaser diode according to an embodiment of this invention;

[0154]FIG. 108 is a diagram showing the constitution of an optical-fibertelecommunication system that uses a long-wavelength surface-emissionlaser diode according to an embodiment of this invention;

[0155]FIG. 109 is a diagram showing the constitution of an optical-fibertelecommunication system that uses a long-wavelength surface-emissionlaser diode according to an embodiment of this invention;

[0156]FIGS. 110A and 110B are diagrams showing an emission angle of alaser diode according to an embodiment of this invention;

[0157] FIGS. 111A-111C are diagrams showing an optical fiber bundleaccording to an embodiment of this invention;

[0158]FIG. 112 is a diagram showing an optical fiber bundle according toan embodiment of this invention;

[0159]FIGS. 113A and 113B are diagrams showing the cross-section of anoptical fiber for multimode transmission according to an embodiment ofthis invention;

[0160]FIG. 114 is a diagram showing the cross-section of an opticalfiber for single mode transmission according to an embodiment of thisinvention;

[0161]FIG. 115 is a diagram showing the electric current-optical outputcharacteristic of a long-wavelength surface-emission laser diode of anembodiment of this invention for each temperature;

[0162]FIG. 116 is a diagram explaining the electric current control of along-wavelength surface-emission laser diode of an embodiment of thisinvention;

[0163]FIG. 117 is a diagram showing the constitution of along-wavelength surface-emission laser diode according to an embodimentof this invention that uses an electric current control;

[0164]FIG. 118 is a diagram showing the interior of an optical fibertelecommunication apparatus in which a long-wavelength surface-emissionlaser diode of an embodiment of this invention is provided;

[0165]FIG. 119 is a diagram showing the constitution of along-wavelength surface-emission laser diode module according to anembodiment of this invention;

[0166]FIG. 120 is a diagram showing the constitution of along-wavelength surface-emission laser diode according to an embodimentof this invention;

[0167]FIG. 121 is a diagram showing the constitution of along-wavelength surface-emission laser diode module according to anembodiment of this invention;

[0168]FIG. 122 is a diagram showing an example of laser chip that isused in this invention;

[0169]FIG. 123 is a diagram showing a different example of laser chipthat is used in this invention;

[0170]FIG. 124 is a diagram showing an example of system of thisinvention;

[0171]FIG. 125 is a diagram showing the constitution of such a laserchip that explains the system of this invention;

[0172]FIG. 126 is a diagram showing an example of control system of thisinvention;

[0173]FIG. 127 is a diagram showing a different example of the controlsystem of this invention;

[0174]FIG. 128 is a diagram explaining the system of this invention;

[0175]FIG. 129 is another diagram explaining the system of thisinvention;

[0176]FIG. 130 is a diagram showing the production process of a laserarray module that uses the long-wavelength surface-emission laser diodeaccording to an embodiment of this invention;

[0177]FIG. 131 is a diagram explaining the quality control process usedin the production process of FIG. 13o.

DETAILED EXPLANATION OF PREFERRED EMBODIMENTS

[0178] [First Embodiment]

[0179] First, a light-emitting device used in an optical-fibertelecommunication system of this invention will be explained withreference to FIG. 1.

[0180]FIG. 1 shows an example of a long-wavelength surface-emissionlaser diode that oscillates at the wavelength of 1.1-1.7 ìm in which thetransmission loss becomes minimum.

[0181] As explained before, while there have been some suggestions aboutthe possibility of long-wavelength surface-emission laser diode thatoscillating at the wavelength of 1.1-1.7 ìm, there have been noknowledge available with regard to the material and constitution for therealization such a laser diode.

[0182] This invention provides concrete constitution of such along-wavelength surface-emission laser diode that uses a material ofGaInNAs system for the active layer.

[0183] In this invention, a high refractive index layer and a lowrefractive index layer of n-type AlGaAs respectively having acomposition represented by AlxGa1-xAs (x=1.0) and AlyGa1-yAs (y=0) arestacked on an n-type GaAs substrate 11 having a (100) surfaceorientation alternately and repeatedly for 35 periods with a thicknessλ/4 for each layer, wherein the λ/4 thickness is a thickness of 1/4times the oscillation wavelength λ of the laser diode. As a result, ann-type semiconductor Bragg reflector (AlAs/GaAs lower semiconductorBragg reflectors) 12 is formed on the GaAs substrate 11.

[0184] Next, an n-type GaInPAs layer 13 having a composition representedas GaxIn1-xPyAs1-y (x=0.5, y=1), is provided on the Bragg reflector 12with a thickness of λ/4. In this example, this n-type GaxIn1-xPyAs1-y(x=0.5, y=1) layer 13 also constitutes one of the low refractive indexlayers that forms a part of the lower part reflector 12.

[0185] Further, a lower part spacer layer 14 of undoped GaAs is formedon the GaInPAs layer 13, and an active layer 15 having a multiplequantum well structure, in which three quantum well layers 15 a eachhaving a composition represented as GaxIn1-xAs are stacked on the lowerpart spacer layer 14 with a GaAs barrier layer 15 b having a thicknessof 20 nm interposed therebetween. Further, an upper part spacer layer 16of undoped GaAs is provided on the active layer 15. The active layer 15forms a resonator 15R having a thickness A corresponding to one fullwavelength of oscillation wavelength of the laser diode together withthe upper and lower spacer layers 14 and 16. It should be noted that theresonator 15R constitutes the active region of the surface-emissionlaser diode.

[0186] In the constitution of FIG. 1, a p-type GaInPAs layer 17 dopedwith C (carbon) and having a composition of GaxIn1-xPyAs1-y (x=0.5, y=1)is formed further on the spacer layer 16. Further, a Zn-doped GaAs layerhaving a composition of AlxGa1-xAs (x=0) and a Zn-doped AlAs layerhaving a composition represented as AlxGa1-xAs (x=1.0) are formed on thep-type GaInPAs layer 17 alternately with a thickness of 1/4 times theoscillation wavelength λ in each medium, to form a periodical structure(one period).

[0187] Further, a semiconductor Bragg reflector 18 is formed thereon bystacking a C-doped, p-type AlGaAs layer having a composition representedas AlxGa1-xAs (x=0.9) and a Zn-doped, p-type GaAs having a compositionrepresented as AlxGa1-xAs (x=0) alternately each with a thickness of 1/4times the oscillation wavelength λ of the laser diode in each medium, toform a periodic structure (25 periods). In this example, the p-typeGaInPAs layer 17 also forms one of the low refractive index layersconstituting a part of the upper part reflector.

[0188] In this embodiment, each of the upper part reflector 18 and thelower part reflector 12 has the constitution of stacking a lowrefractive index layer and a high refractive index layer alternately,wherein it should be noted that a heterospike buffer layer having acomposition represented as AlzGa1-zAs (0≦y<z<x≦1) and a refractive indexintermediate between the low refractive index layer and the highrefractive index layer is interposed in this invention between the lowrefractive index layer and the high refractive index layer as shown inFIG. 2.

[0189] Hereinafter, description will be made about the constitution ofthe reflector of the present invention that reflects the wavelength of1.1 ìm or more in detail with reference to FIG. 2.

[0190]FIG. 2 shows a part of the semiconductor Bragg reflector 18. Asimilar constitution is formed also for the semiconductor Braggreflector 12. In the description below, explanation for the Braggreflector 12 will be omitted in view of the essentially sameconstitution of the reflector 18 and the reflector 12.

[0191]FIG. 2 shows an example of the reflection spectrum of thereflector in which a structural unit of AlAs/GaAs is repeated 24 times(24 pairs). In the example of FIG. 2, each of the AlAs layers is formedto have a thickness of 93.8 nm and each of the GaAs layers is formed tohave a thickness of 79.3 nm, wherein it should be noted that thesethicknesses are chosen so as to be equal to 1/4n wavelength of theoptical radiation that has a wavelength of 1.1 μm in the vacuumenvironment. Here, n represents the refractive index of each of the AlAslayer and the GaAs layers. By setting the thickness of the layersconstituting the distributed Bragg reflector to be equal to 1/4n-timesof a given wavelength λ, it is possible to tune the reflector to thiswavelength λ, and the distributed Bragg reflector thus tuned shows alarge reflectance in the wide wavelength band including the foregoingtuned wavelength λ. This wavelength λ will be referred to as designedwavelength.

[0192] It should be noted that the material of the AlGaAs system hasvarious advantages for the material of the distributed Bragg reflector.For example, the AlGaAs material can be grown on a commonly availablelow-cost GaAs substrate with lattice matching. Further, the material hasexcellent heat radiation capability as compared with other semiconductormaterials. Furthermore, by using the material system of AlGaAs, itbecomes possible to secure a large diffractive index as compared withthe case of using other material systems. For example, a refractiveindex difference of 0.5 is realized between the end member compositionsAlAs and GaAs that constitute the AlGaAs system at the wavelength of 1.3μm. Thus, it becomes possible to achieve a large reflectance withreduced number of stacked pairs as compared with the case of using othermaterial system.

[0193]FIG. 3 shows the construction of the distributed Bragg reflectorconstituting the upper reflector 18 or lower reflector 12 of the laserdiode of FIG. 1.

[0194]FIG. 3 is referred to.

[0195] In the present embodiment, each of the upper and lower reflectors18 and 12 is formed of a distributed Bragg reflector having a reflectionwavelength of 1.1 μm or more and has a construction of stacking a lowerrefractive index layer 18 a and an upper refractive index layer 18 b,wherein it can be seen that there is provided a heterospike buffer layer18 c of AlxGa1-xAs (0≦y<z<z≦1) having a refractive index intermediatebetween the refractive index of the low refractive index layer 18 a andthe high refractive index layer 18 b.

[0196] Such a heterospike buffer layer has been studied in relation tothe laser diode of 0.85 ìm band. However, it is still in the stage offeasibility study and no detailed study has been made with regard to thematerial, thickness, and like of the heterospike buffer layer. Further,there has been no proposal at all about such a heterospike buffer layerin relation to the long-wavelength surface-emission laser diode of1.1-1.7 ìm band as in the case of this invention. This is because thelong-wavelength surface-emission laser diode of 1.1-1.7 ìm band itselfis a new field and few researches have been made so far.

[0197] The inventor of this invention noticed the usefulness of opticaltelecommunication technology that uses a long-wavelengthsurface-emission laser diode of 1.1-1.7 ìm band and devotedly conducteda study so as to realize such a laser diode.

[0198] Such a heterospike buffer layer 18 c is formed at the time offormation of the semiconductor Bragg reflector 12 or 18 by an MOCVDprocess, by controlling the source gas flow rate, such that the Alcontent in the AlGaAs film forming the heterospike buffer layer changescontinuously or stepwise. With this, the refractive index of a filmchanges also continuously or stepwise.

[0199] In more detail, the supply rate of Ga and Al is changed such thatthe value of the compositional parameter z is changed in the AlzGa1-zAs(0≦y<z<x≦1) layer from 0 to 1.0, at the time of the formation of theAlGa s film 18 c. With this, the film composition of the heterospikebuffer layer changes gradually from GaAs to AlGaAs to AlAs. Such achange of the supply rate is caused by controlling the gas flow rate atthe time of the formation of film 12 c as noted before. A similar effectis obtained when the ratio of Al and Ga is changed stepwise orcontinuously.

[0200] The reason that such a heterospike buffer layer is provided is toeliminate the problem of is increased resistance, which appears in asemiconductor Bragg reflector, particularly in a p-type semiconductorBragg reflector such as the Bragg reflector 18. Such increase ofelectric resistance is caused as a result of hetero barrier formed atthe hetero interface where two different semiconductor layers of thesemiconductor Bragg reflector make a contact. By changing the Alcomposition gradually at the hetero interface from the low refractiveindex layer to the high refractive index layer as in the case of thisinvention, there is also caused a corresponding gradual change ofrefractive index at the hetero interface. In this way, the occurrence ofthe hetero barrier at the hetero interface is successfully suppressed.

[0201] Hereinafter, more detailed explanation will be made about such aheterospike buffer layer with reference to FIG. 4.

[0202]FIG. 4 shows an example of the semiconductor Bragg reflector 18provided with the heterospike buffer layer 18 c between twosemiconductor layers 18 a and 18 b constituting the semiconductor Braggreflector. It should be noted that FIG. 4 shows the case of using thesemiconductor material AlzGa1-zAs (0≦y<z<x≦1) of the AlGaAs system forthe material of the semiconductor Bragg reflector.

[0203] The two semiconductor layers 18 a and 18 b constituting thesemiconductor Bragg reflector 18 of FIG. 4 are AlAs and GaAs, and acompositional gradation layer changing the Al content gradually thereinis provided between the layers 18 a and 18 b as the heterospike bufferlayer. The heterospike buffer layer thus formed has valence band energyintermediate between the valence band energy of AlAs and the valenceband energy of GaAs. Thus, the ratio of Al to Ga is changed from GaAs toAlGaAs to AlAs in the heterospike buffer layer, and the value of z ofthe AlzGa1-zAs (0≦y<z<x≦1) heterospike buffer layer is changed graduallyfrom 0 to 1.0.

[0204] In the semiconductor material of the AlGaAs system, the bandgapenergy increases with the Al content and the refractive index falls offwith the Al content In the conduction band, there occurs an increase ofband energy until the Al content x reaches 0.43, and the band energystarts to decrease thereafter. In the valence band, on the other hand,the valence band energy falls off monotonously with the increment of theAl content x. In total, the bandgap energy increases with the Al contentx.

[0205] In the case of the quaternary system of AlGaInP, a similar trendas in the case of increasing the Al content in the AlGaAs system appearswith increase of the AlInP composition, and the conduction band energyincreases up to the point in which the AlInP composition has reached0.7. Thereafter, the conduction band energy starts to decrease. On theother hand, the valence band energy decreases monotonously with theincrease of AlInP composition.

[0206] In the example of FIG. 4, it should be noted that the rate of thecompositional gradation (rate of increase of bandgap energy) is setlarger in the region near the GaAs layer (region I in FIG. 4) ascompared with the region near the AlAs layer (region II in FIG. 4). Forthe purpose of comparison, a structure having a linear compositionalgradation layer, in which the Al content therein is changed onlylinearly, for the heterospike buffer layer 18 c is shown in FIG. 5.

[0207]FIG. 6 shows the result of evaluation of the electric resistanceof the p-type distributed Bragg reflector 18 tuned to the reflectionwavelength of 1.3 μm, wherein the Bragg reflector 18 is formed byrepeating the AlAs/GaAs unit structure, including therein theheterospike buffer layer of 20 nm is thickness between the AlAs layer 18a and the GaAs layer 18 b, four times (four pair stacking).

[0208] In FIG. 6, each of the layers 18 a-18 c of the distributed Braggreflector 18 including the heterospike buffer layer 18 c is formed of ap-type layer having a career density of 1×10¹⁸ cm⁻³, and the verticalaxis of FIG. 6 represents the value of differential sheet resistance atnear zero bias state. On the other hand, the horizontal axis of FIG. 6represents the Al compositional gradation in the region I. It should benoted that the “Al compositional gradation” is defined as the change ofthe Al content in the region I divided by the thickness of the region I.Thus, FIG. 6 represents the case in which the thickness of the region Iis changed variously, while it should be noted that the total thicknessof the region I and the region II is maintained constant at 20 nm. Thus,the thickness and the compositional gradation of the region II aredetermined by the thickness and the compositional gradation of theregion I. The Al compositional gradation for the case a simple linearcompositional gradation layer is provided between the GaAs layer and theAlAs layer becomes 0.05 nm⁻¹ This hits the A point of the drawing.

[0209] From FIG. 6, it can be seen that the resistance is reducedfurther by increasing the Al compositional gradient in the heterospikebuffer layer 18 c from the region II to the region I as compared withthe case of FIG. 5 in which the compositional gradation is linearthroughout the heterospike buffer layer 18 c. Also, it can be seen thatthere exists an optimum Al compositional gradation in which theresistance becomes minimum. For example, in the case the thickness ofthe region I is 10 nm (the same thickness as the region II), it can beseen that the resistance is reduced to about 80% of the conventionalresistance value obtained for the case in which the Al compositionalgradation is set to 0.09 nm⁻¹ This trend does not change depending onthe applied voltage.

[0210] Next, the reason of this will be explained.

[0211]FIG. 7 shows the valence band structure of the distributed Braggreflector having the AlAs/GaAs structure for the part near the heterosurface in thermal equilibrium state.

[0212]FIG. 7 is referred to.

[0213] It can be seen that the heterospike originating from the banddiscontinuity appear predominantly at the side of the widegap AlAslayer. In the side of the GaAs layer, the occurrence of the notch istrifling. Thus, the notch at the side of the GaAs layer does not becomethe cause of increase of resistance. Therefore it is concluded that, forthe reduction of resistance of a distributed Bragg reflector, it isimportant to eliminate or reduce the heterospike appearing at the sideof the AlAs layer within a limited thickness of the heterospike bufferlayer.

[0214] In the structure of FIG. 7, it can be seen that the Al content ofthe heterospike buffer layer 18 c is increased sharply at the side ofthe GaAs layer 18 b in which there occurs the notch formation, whilethis corresponds to a gentle compositional gradient at the side of theAlAs layer, in side which the remarkable heterospike formation takesplace. By doing so, it becomes possible to reduce the spike formation ascompared with the case of changing the composition of the heterospikebuffer layer linearly as in the case of FIG. 5. When the Alcompositional gradation is set smaller in the region I with regard tothe region II, on the other hand, there occurs an unwanted increase ofresistance.

[0215]FIG. 8 shows the valence band diagram of the structures of FIGS. 3and 4 in a thermal equilibrium state, wherein the continuous linerepresents the band structure of FIG. 3 while the dotted line representsthe band structure of FIG. 4.

[0216]FIG. 8 is referred to. By using the compositional gradationprofile of FIG. 4, it becomes possible to reduce the compositionalgradation of the heterospike buffer layer 18 c in the region II at theside of the AlAs layer 18 a with regard to the region I at the side ofthe GaAs layer 18 b as compared with case of using the simplecompositional gradation of FIG. 5 with the same thickness. Thus, it isconcluded that the resistance of the semiconductor distributed Braggreflector is reduced by increasing the compositional gradation in theregion I of the heterospike buffer layer I.

[0217] In the example of FIG. 4, it can be seen that the heterospikebuffer layer 18 c is formed of two regions I and II each having a linearAl compositional profile. On the other hand, it is also possible tochange the Al content non-linearly as represented in FIG. 9. Even insuch a case, it is possible to define the boundary between the regions Iand II as an intersection of the intercept drawn to the valence band atthe boundary between the GaAs layer 18 b and the heterospike bufferlayer 18 c and the intercept drawn also to the valence band at theboundary between the AlAs layer 18 a and the heterospike buffer layer 18c, as represented in FIG. 9.

[0218] In the heterospike buffer layer 18 c, it is not necessary thatthe Al composition changes continuously but another layer may existbetween the regions I and I as represented in FIG. 10.

[0219] According to FIG. 6, the differential sheet resistance of theBragg reflector is reduced with decreasing thickness of the region I.Further, it can be seen that the minimum of the differential sheetresistance is achieved when there is no region I provided as representedin FIG. 11 or when the thickness of the region I is small enough that itcan be regarded that there is a discontinuity in the conduction bandbetween the GaAs layer 18 b (narrow gap layer) and the heterospikebuffer layer 18 c (widegap layer) as represented in FIG. 12.

[0220]FIG. 13 shows the differential sheet resistance of the distributedBragg reflector similar to the one shown in FIG. 6 as a function of theAl compositional gradation in the region II. It should be noted that theAl compositional gradation in the region II is determined uniquely fromthe Al compositional gradation in the region I and the thickness of theregion I.

[0221] From FIG. 13, it can be seen that there appears a minimum of thedifferential sheet resistance at a particular value of the compositionalgradation in the layer 11, wherein this particular value of thecompositional gradation is irrelevant to the thicknesses of the regionsI and II.

[0222]FIG. 14, on the other hand, shows a similar relationship as thecase of FIG. 13 for the case the total thickens of the regions 1 and 11is 40 nm.

[0223] Referring to FIG. 14, it can be seen that a similar minimum ofresistance appears at a particular value of the Al compositionalgradation.

[0224] From FIGS. 13 and 14, it is possible to evaluate the optimumdiscontinuity of valence band energy between the narrow gap layer (GaAslayer 18 b of FIG. 3) and the heterospike buffer layer 18 c forminimizing the resistance of the distributed Brag reflector having aheterospike buffer layer.

[0225] As noted above, in the semiconductor distributed Bragg reflectorhaving a heterospike buffer layer, it is possible to minimize theresistivity of the reflector by changing the Al composition of theheterospike buffer layer sharply in the region I and optimizing the Alcompositional gradation in the region I correspondingly, such that thereappears a discontinuity or substantial discontinuity at the boundarybetween the narrow gap layer 18 b and the heterospike buffer layer 18 c.

[0226] For example, it is possible to reduce the resistance of thedistributed Bragg reflector by about 75% by reducing the thickness ofthe region I to 1 nm in the heterospike buffer layer 18 c having athickness of 20 nm, as compared with the distributed Bragg reflectorhaving a heterospike buffer layer of the same thickness except that theAl composition is changed linearly throughout the heterospike bufferlayer.

[0227] In this case, too, it is not necessary that the Al contentchanges linearly in the regions I and II of the heterospike buffer layer18 c but the Al content may be changed non-linearly as represented inFIG. 15.

[0228] Further, it should be noted that the foregoing consideration isnot limited to the distributed Bragg reflector of the AlGaAs system butis applicable also to the distributed Bragg reflector of other materialsystems such as AlGaInP system. In the case of the distributed Braggreflector of the AlGaInP system, it is possible to achieve a similareffect by changing the AlInP composition in the heterospike bufferlayer.

[0229] Next, the optimum thickness of such a heterospike buffer layerAlzGa1-zAs (0≦y<z<x≦1) will be described.

[0230]FIG. 16 shows the relationship between the reflectance andthickness of the heterospike buffer layer for a distributed Braggreflector tuned to the 0.88 μm band and 1.3 μm band for the case theheterospike buffer layer 18 c has a linear compositional profile of Alas represented in FIG. 5. The reason that the reflector tuned to theconventional wavelength of 0.88 μm was prepared in this experiment is tomake a comparison with a conventional reflector tuned to thiswavelength. It should be noted that GaAs absorbs optical radiationshorter than 0.87 μm. In FIG. 16, GaAs is used for the high refractiveindex layer and AlAs is used for the low refractive index layer.

[0231] The distributed Bragg reflector thus produced needed 18 pairs ormore of the low refractive index layer and the high refractive indexlayer in order to achieve the reflectance exceeding 99.9% at thewavelength band of 0.88 μm, while 23 pairs or more were needed forachieving the same reflectance at the wavelength band of 1.3 μm. Itshould be noted that FIG. 16 represents the relationship between thereflectance and thickness of the heterospike buffer layer of thedistributed Bragg reflector tuned to the respective wavelengths.

[0232] Table 1 summarizes the reflectance of FIG. 16. TABLE 1 0 nm 5 nm10 nm 0.88 μm band 99.914 99.912 99.905  1.3 μm band 99.923 99.92399.920

[0233] Referring to Table 1, it can be seen that there is no decrease ofreflectance in the 1.3 μm band until the thickness of the heterospikebuffer layer 18 c reaches 5 nm. In the 0.88 μm band, on the other hand,there starts a decrease of reflectance at the thickness of 5 nm of theheterospike buffer layer 18 c. In the case of a surface emission laserdiode, the cavity length is characteristically small and the effect ofreflection loss by the mirror appears conspicuously. Thus, even in thecase the decrease of the reflectance is very small, a large effect iscaused in the threshold current of the laser diode.

[0234]FIGS. 17 and 18 show the resistivity of the AlAs/GaAs distributedBragg reflector, having the heterospike buffer layer 18 c similar toFIG. 5 and tuned to the reflection wavelength of 1.3 μm, near the zerobias point. In the drawings, the resistivity is represented in terms ofΩcm² and is defined as dV/dJ (V: voltage represented in terms of volts;J: current density represented in terms of A/cm²). In the illustratedexample, the number of pairs is four. It should be noted that FIG. 17and FIG. 18 shows essentially the same diagram except that FIG. 17 showsthe diagram in the logarithmic representation while FIG. 18 shows thediagram in the linear scale representation. In FIGS. 17 and 18, thebroken line represents the resistivity evaluated from the bulk crystalresistivity, neglecting the effect of the band discontinuity. Further,each layer of the distributed Bragg reflector is doped to the p-typewith the carrier density of 1×10¹⁸ cm⁻³.

[0235] Referring to FIG. 17, it can be sent hat the resistivity of thedistributed Bragg reflector decreases with the thickness of theheterospike buffer layer 18 c. In the case of the reflector tuned to thewavelength of 1.3 μm, the proportion of the compositional gradationlayer 18 c with regard to the rest of the layers lea and 18 b isrelatively small. Thus, it becomes possible to reduce the resistivity bytwo orders by providing the heterospike buffer layer 18 c with thethickness of 5 nm, without causing influence to the reflectance. Longerthe reflection wavelength, the heterospike buffer layer 18 c can beformed with increased thickness. When the thickness is smaller than 5nm, on the other hand, the desired reduction of the resistance is notobtained as can be seen from FIG. 17.

[0236] As represented in FIG. 17, the distributed Bragg reflector showsa very high resistivity value of 1 Ωcm² when the heterospike bufferlayer 18 c is omitted. Thus, in the matter of practical problems, it isextremely difficult to drive a laser diode having a distributed Braggreflector in which 20 or more stacks are provided. In order to drivesuch a laser diode, a very high voltage would be needed. Thus, it isdifficult to apply such a distributed Bragg reflector to a currentdriven device such as a surface-emission laser diode.

[0237] In the case of providing the heterospike buffer layer 18 c withthe thickness of 5 nm as noted above, the resistance of the reflector isreduced by two orders as compared with the case not providing such aheterospike buffer layer. As a result, supply of the drive current tothe laser diode is facilitated and laser oscillation becomes possible.Further, the necessary drive voltage is reduced, and the problems suchas failure or malfunctioning of the laser diode or reliability areresolved. As represented in Table 1, there is no decrease ofreflectance. Thus, the laser oscillation can be achieved at a lowthreshold current density.

[0238] Thus, the foregoing thickness of 5 nm is thought as being thelower limit of the heterospike buffer layer that enables decrease ofresistance without causing problems to the reflection performance atlong wavelengths. Therefore, the heterospike buffer layer 18 c should beformed with a thickness of 5 nm or more.

[0239] By increasing the thickness of the heterospike buffer layer 18 c,the resistivity falls of sharply, and with this, the drive voltage andthe heat generation of the device are reduced. Associated with this, theoperational temperature range of the laser diode is extended and thelaser output is increased.

[0240] In the case of allowing 99.8% reflectance for the distributedBragg reflector, the maximum thickness of the heterospike buffer layerthat can be provided to the distributed Bragg reflector tuned to the0.88 μm wavelength is limited to 20 nm or less. In the case of thedistributed Bragg reflector tuned to the 1.3 μm, it is possible toprovide the heterospike buffer layer 18 c up to the thickness of 50 nm.

[0241] As represented in FIG. 6, the resistance of the distributed Braggreflector decreases with the thickness of the heterospike buffer layer18 c up to the thickness of 50 nm for the heterospike buffer layer 18 c,and a resistivity of 1.05 times the bulk resistivity is achieved at thethickness of 50 nm for the layer 18 c. When the thickness of theheterospike buffer layer 18 c is increased further, on the other had,there appears a saturation in the decrease of the resistivity.

[0242] It should be noted that the reflectance of the distributed Braggreflector starts to decrease sharply with increase of thickness of theheterospike buffer layer 18 c, and the reflectance is reduced to thelevel of 99.8% or les when the thickness of the layer 18 c has exceeded50 nm. Thus, it is necessary to limit the thickness of the heterospikebuffer layer 18 c to be 50 nm or less in order to satisfy therequirement of high reflectance and low resistivity simultaneously.

[0243]FIG. 19 shows the reduction of the reflectance in detail, whereinFIG. 19 shows the change rate of the reflectance R (dR/dt) with regardto the thickness t of the heterospike buffer layer 18 c.

[0244] Referring to FIG. 19, it can be seen that there occurs a sharprise of the reflectance when the thickness of the heterospike bufferlayer has exceeded 50 nm. With this, there occurs an increase of thethreshold current of laser oscillation.

[0245] Thus, in the distributed Bragg reflector tuned to the wavelengthof 1.3 μm and having a heterospike buffer layer having a thickness of 5nm or more but 50 nm or less, it is possible to reduce the resistancecaused by the heterointerface while maintaining a high reflectance. Byusing such a distributed Bragg reflector in a surface-emission. laserdiode, it is possible to achieve a laser oscillation under a practicaldrive condition.

[0246] In the case of a surface-emission laser diode, it is necessary todesign the reflector such that the distributed Bragg reflector 18 at theexit side has a relatively smaller reflectance for facilitating opticaloutput in order to increase the output power of the laser diode.Further, in order to obtain a stable laser oscillation up to the highoutput region (high level injection region), it is necessary to set theoutput saturation point as high as possible by suppressing the deviceheat generation. The distributed Bragg reflector having a relativelythick (50 nm) heterospike buffer layer 18 c of the present inventionsatisfies these conditions and is suited for use in a high-power laserdiode.

[0247] Thus, according to the long-wavelength surface-emission laserdiode of the present invention, it is possible to optimize thereflectance and electric properties of the distributed Bragg reflectorused therein by optimizing the thickness of the heterospike buffer layer18 c within the range of 5-50 nm.

[0248] In the example of FIG. 3, the low refractive index layer 18 a isformed of an AlAs layer and the high-refractive index layer 18 b isformed of a GaAs layer. On the other hand, it is also possible to usetwo AlGaAs layers for the low-refractive index layer 18 a and the highrefractive index layer 18 b, by changing the Al content in the AlGaAslayers. In this case, it is preferable to increase the difference of theAl content between the low-refractive index layer 18 a and the highrefractive index layer 18 b for decreasing the number of stacks in thereflector, as the reflectance of the reflector is increased withincreasing degree of difference of the refractive index between the lowrefractive index layer and the high refractive index layer. Thus, itwill be noted that the construction of FIG. 3 provides the maximumrefractive index difference between the low refractive index layer andthe high refractive index layer by using GaAs and AlAs.

[0249] As noted already, in the heteroepitaxial structure in which thereis a large difference of Al content between the low refractive indexlayer and the high refractive index layer, the band discontinuity at thevalence band is also increased and there arises a problem of increaseddevice resistance in trade off to the increase of the reflectance. Thus,in such a case, it is necessary to provide the heterospike buffer layerof sufficiently large thickness between the high refractive index layer18 b and the low refractive index layer 18 a for reducing theresistivity of the reflector However, use of such a heterospike bufferlayer has been difficult in the conventional distributed Bragg reflectortuned to the wavelength band of 0.85 μm. In the present invention, onthe contrary, it is possible to achieve a high reflectance andsimultaneously a low resistance while using the material system ofGaAs/AlAs for the distributed Bragg reflector.

[0250] In the distributed Bragg reflector of FIG. 3, it is possible toform the heterospike buffer layer 18 c in the range of 20-50 nm in thecase the reflector is tuned to the reflection wavelength of 1.1 μm ormore.

[0251] Referring to FIG. 17 again in more detail, it can be seen thatthe resistivity of the distributed Bragg reflector decreases sharplywith increase of the thickness of the heterospike buffer layer 18 c andthen approaches gradually to the bulk resistivity. In the example ofFIG. 17, the threshold thickness of the heterospike buffer layer 18 cabove which the saturation of resistivity takes place is about 20 nm. Atthis thickness of 20 nm, it can be seen that the resistivity is reducedto about twice the bulk resistivity. Thus, by using the thickness of 20nm or more but 50 nm or less, it is possible to obtain a distributedBragg reflector having a resistivity comparable to the bulk resistivity.

[0252]FIG. 20 shows a band structure for another distributed Braggreflector In the example of FIG. 20, GaAs is used for thehigh-refractive index layer 18 b in the structure of FIG. 3 while thelow refractive index layer 18 a formed of Al_(0.8)Ga_(0.2)As. Further,the example of FIG. 20 uses a compositional gradation layer having athickness of 30 nm for the heterospike buffer layer 18 c. In the exampleof FIG. 20, the compositional gradation layer is formed such that thevalence band energy changes parabolic with the thickness. In such aparabolic compositional gradation layer, the valence band energy has adownwardly convex shape.

[0253] In the construction of FIG. 20, it should be noted that thedesign wavelength (λ) of the distributed Bragg reflector is 1.5 μm, andthe thickness of the Al_(0.8)Ga_(0.2)As layer 18 a and the thickness ofthe GaAs layer 18 b are respectively chosen to 110.8 nm and 12.55 nm soas to be equal to λ/4n, wherein n is a refractive index in therespective layers.

[0254] In the distributed Bragg reflector of FIG. 20, each of thesemiconductor layers is formed to have a thickness subtracted with theoptical thickness of the parabolic compositional gradation layer 18 cfrom the above noted thickness. In the case an Al_(0.6)Ga_(0.4)As layeris used for the low-refractive index layer 18 a as in the case of theembodiment to be described later, the λ/4n thickness of theAl_(0.6)Ga_(0.4)As layer for the distributed Bragg reflector tuned tothe 1.5 μm wavelength becomes 121.7 nm.

[0255] In the present embodiment, each of the Al_(0.8)Ga_(0.2)As layer18 a, the GaAs layer 18 b and the parabolic compositional gradationlayer 18 c is doped to the p-type such that each of the foregoing layershave a uniform carrier densitv of 5×10¹⁷ cm⁻³.

[0256] Thus, in the present embodiment, the resistivity of thedistributed Bragg reflector is reduced to the value generally equal tothe bulk resistivity in spite of the fact that the-distributed Braggreflector is doped to a relatively small doping density of 5×10¹⁷ cm⁻³due to the use of the relatively thick compositional gradation layer 18c (50 nm). The use of such a low doping density is also advantageous inview of reduced optical absorption caused by the transition between thevalence bands. It should be noted that, in such a distributed Braggreflector tuned to the longer wavelength of 1.5 μm, it is easy toprovide a thick parabolic compositional gradation layer 18 c whilemaintaining high reflectance.

[0257] While a compositional gradation layer having a parabolicgradation is used for the heterospike buffer layer 18 c in theembodiment of FIG. 20, the heterospike buffer layer 18 c may be formedof another layer. Further, the distributed Bragg reflector may be tunedto the wavelength other than 1.5 μm. Similarly, the Al composition ofthe low-refractive index layer may be different from the one explainedabove. Further, the doping density may be changed in each of the layersin the distributed Bragg reflector.

[0258] As noted above, the resistance of the distributed Bragg reflectortuned to the long wavelength band of 1.1 μm or more is reduced sharplywhen the thickness of the heterospike buffer layer 18 c is increased asis represented in FIG. 17, until the thickness of the heterospike bufferlayer 18 c exceeds a predetermined thickness. This predeterminedthickness of the heterospike buffer layer 18 c within which the sharpchange of the resistivity takes place is related to the doping densityused in the distributed Bragg reflector.

[0259]FIG. 21 shows the case the doping density of 7×10¹⁷ cm⁻³ is usedin the AlAs/GaAs distributed Bragg reflector of FIG. 20 for each of thelayers therein.

[0260] Referring to FIG. 21 in which the doping density is reduced, itcan be seen that the thickness range of the heterospike buffer layer 18c in which there occurs a sharp drop of the resistivity in thedistributed Bragg reflector has been increased to 30 nm. When theforegoing limit is exceeded, it can be seen that the resistivity ischanged linearly to the value of the bulk resistivity. Particularly, inthe case of a p-type distributed Bragg reflector, there occurs anincrease of optical absorption when the hole density (doping density) isincreased as a result of optical absorption between the valence bands inaddition to the free carrier absorption. Thus, when such a distributedBragg reflector is applied to a laser diode, there is caused an increaseof the laser threshold current.

[0261] Thus, from the viewpoint of optical absorption, it is preferableto use a low carrier density As the effect of the transition between thevalence bands appears conspicuous for optical radiation of longwavelengths, it is important to suppress the absorption loss in the longwavelength laser diode operating at the wavelength of 1.1 μm or more. Inthe case of a conventional distributed Bragg reflector having a dopingdensity exceeding 1×10¹⁸ cm⁻³, it is difficult to reduce the absorptionloss.

[0262] Because of this reason, there are cases in which the dopingdensity is reduced to 1×10¹⁸ cm⁻³ or less in one of the low refractiveindex layer 18 a, the high refractive index layer 18 b, the heterospikebuffer layer 18 c, or all of the layers 18 a-18 c. In such a distributedBragg reflector in which the doping density is reduced, however, thereoccurs an increase of extension of the depletion layer, and the problemof increase of resistance is inevitable. When the doping density is thusreduced, therefore, it is necessary to increase the thickness of theheterospike buffer layer, while it is noted that such a compensatingeffect of the heterospike buffer layer appears when the thicknessthereof has reached 30 nm or more. In the case the doping density isreduced further, a more thick heterospike buffer layer 18 c is needed.In such a case, the effect of the hetero interface is compensated for byusing a larger thickness for the heteroepitaxial buffer layer within theforegoing range, such as 40 nm or 50 nm. A similar argument applies alsoto the case when AlGaAs is used in place of AlAs in the distributedBragg reflector.

[0263]FIG. 22 shows the result of calculation of resistivity of thedistributed Bragg reflector including 4 pairs of theAl_(0.8)Ga_(0.2)As/GaAs structure. In the example of FIG. 22, the dopingdensity of each layer is reduced further to the level of 5×10¹⁷ cm⁻³.

[0264] In this case, too, the heterospike buffer layer 18 c has athickness of 30 nm or more and it can be seen that the resistivity ofthe distributed Bragg reflector is comparable to the resistivity of thebulk resistivity. In the case of a distributed Bragg reflector in whichany or all of the high refractive index layer 18 a, low refractive indexlayer 18 b and the heterospike buffer layer 18 c are set smaller thanthe conventional doping density of 1×10¹⁸ cm⁻³, for example, thereappears a saturation of resistivity when the thickness of theheterospike buffer layer 18 c has reached 30 nm. Thus, in the case atleast one of the layers constituting the distributed Bragg reflector hasthe doping density of 1×10¹⁸ cm⁻³ or less, it is possible to decreasethe resistance effectively by using the heterospike buffer layer havinga thickness in the range of 30-50 nm.

[0265] Of course, the foregoing thickness of the heterospike bufferlayer 18 c is effective also in the distributed Bragg reflector having alarger doping density and may be used in the case all of the layersconstituting the distributed Bragg reflector has a doping density of1×10¹⁸ cm⁻³ or more. On the other hand, it is especially advantageous touse the doping density of 1×10¹⁸ cm⁻³ or less in combination with theheterospike buffer layer having a thickness appropriately chosen fromthe range of 30-50 nm in view of the fact that both the absorption lossand the resistance are reduced.

[0266] By using the distributed Bragg reflector of the embodiment ofFIG. 22 for the reflector in the surface-emission laser diode, it ispossible to obtain a surface-emission laser diode having a superiorcharacteristic. As noted before, it has been difficult to realize thethickness of 30-50 nm for the heterospike buffer layer in theconventional distributed Bragg reflector tuned to the 0.85 μmwavelength. The heterospike buffer layer of this thickness becamepossible for the first time in the distributed Bragg reflector tuned tothe wavelength of 1.1 μm.

[0267] In the distributed Bragg reflector of the present invention, itis also possible to set the difference of Al content between the lowrefractive index layer 18 a and the high refractive index layer 18 b ofthe distributed Bragg reflector to be less than 0.8 by constituting thelayers 18 a and 18 b by any of AlAs, GaAs and AlGaAs mixed crystal.

[0268] When the difference of Al content between the high refractiveindex layer 18 b and the low refractive index layer 18 a is less than0.8 in the distributed Bragg reflector constituted of a semiconductormaterial of the AlGaAs system and tuned to the design wavelength of 1.1μm or longer, it is possible to reduce the electric resistance whilemaintaining a high reflectance.

[0269] In a mixed crystal of AlGaAs, it should be noted that the valenceband energy decreases monotonously with the increase of Al contenttherein, and the band discontinuity of the valence band at the interfaceto a GaAs crystal increases with increasing Al content in the AlGaAsmixed crystal Thereby, there is formed a large potential barrier at thehetero interface, and this potential barrier has been the cause of thehigh resistance of the distributed Bragg reflector. Further, it shouldbe noted that the decrease of the valence band energy is generallyproportional to the Al content, and the band discontinuity between thesemiconductor layers having different Al compositions correspond to theAl compositional difference.

[0270]FIGS. 23 and 24 show the resistivity of the p-type distributedBragg reflector tuned to the design wavelength of 1.3 μm and including 4pairs of high refractive index layer 18 b and low refractive index layer18 a for various thicknesses of the heterospike buffer layer. In FIGS.23 and 24, it should be noted that the distributed Bragg reflector usesGaAs for the high refractive index layer 18 b and AlAs,Al_(0.8)Ga_(0.2)As and Al_(0.6)Ga_(0.4)As have been used for the lowrefractive index layer. Further, each of the layers has been formed tohave a thickness tuned to 1/4 the design wavelength while taking intoconsideration of the refractive index of the respective layers. Further,the doping density is set to 5×10^(17 cm) ⁻³ throughout the layers inFIGS. 23 and 1×10¹⁸ cm⁻³ throughout the layers in FIG. 24. It should benoted that the doping density of 1×10¹⁸ cm⁻³ is used commonly in thedoping of the conventional p-type distributed Bragg reflector.

[0271] From FIGS. 23 and 24, it can be seen that the resistivity of thedistributed Bragg reflector increases with increasing Al content in theAlGaAs layer and decreasing thickness of the heterospike buffer layer,and that it is necessary to provide a thick heterospike buffer layer inorder to reduce the resistivity of the distributed Bragg reflector tothe bulk resistivity level. In the case of the distributed Braggreflector that uses Al_(0.6)Ga_(0.4)As and GaAs as the low refractiveindex layer 18 a and the high refractive index layer 18 b, for example,there appears a band discontinuity of about 300 mev, while the banddiscontinuity increases to about 400 meV when Al_(0.8)Ga_(0.2)As is usedfor the low refractive index layer 18 a and GaAs is used for the highrefractive index layer 18 b.

[0272] From the results of FIGS. 23 and 24, it is concluded that thethickness of 20 nm or more is preferable for the heterospike bufferlayer lc in order to reduce the resistivity of a distributed Braggreflector formed of AlAs layers and GaAs layers in order to reduce theresistivity of the distributed Bragg reflector effectively, althoughthis would also depend on the doping density. Thus, in the case the banddiscontinuity is 400 meV or less, in other words the Al compositionaldifference is less than 0.8, it can be seen that the resistivity of theheterospike buffer layer can be reduced effectively by increasing thethickness of the heterospike buffer layer to 20 nm or more.

[0273] Actually, the increase of resistance of the distributed Braggreflector caused by the band discontinuity depends not only on thebarrier height and barrier thickness but also on the effective mass ofholes used for the carriers. However, there is no large difference inthe effective mass for heavy holes between AlGaAs, AlGaInP and GaInAsP,and the band discontinuity can be regarded as the index of theheterointerface resistance. Thus, in the case the valence banddiscontinuity is less than 400 meV, and hence the Al compositionaldifference is less than 0.8, it is possible to reduce the resistance ofthe distributed Bragg reflector by using the heterospike buffer layerhaving a thickness of 20 nm or more.

[0274] With regard to the upper limit of the heterospike buffer layer 18c, the thickness of the heterospike buffer layer 18 c should be chosen,in view of the tuned wavelength of the distributed Bragg reflector, suchthat no remarkable decrease of reflectance occurs. By doing so, adistributed Bragg reflector having excellent electrical and opticalcharacteristics is obtained.

[0275] In the distributed Bragg reflector having a structure shown inFIG. 3, it is possible to use any of AlAs, GaAs and AlGaAs mixed crystalfor the low refractive index buffer layer 18 a and the high refractiveindex layer 18 b such that the Al compositional difference between thelayers 18 a and 18 b is 0.8 or more.

[0276] In this embodiment, it is also possible to reduce the resistanceof the distributed Bragg reflector effectively while maintaining a highreflectance.

[0277] When AlAs and GaAs are combined for the low refractive indexlayer 18 a and the high refractive index layer 18 b, it should be notedthat there appears a band discontinuity of about 500 meV in the valenceband, and thus, it is necessary to provide a thick heterospike bufferlayer for reducing the resistivity of the distributed Bragg reflector,although the thickness of the heterospike buffer layer may depend on thedoping density. In such a case, it is concluded, in view of the resultsof FIGS. 23 and 24, that the heterospike buffer layer 18 c has athickness of 30 nm or more. Thus, from the view point of banddiscontinuity of the semiconductor materials constituting thedistributed Bragg reflector, it becomes possible to reduce theresistance of the distributed Bragg reflector by setting the thicknessof the heterospike buffer layer to be 30 nm or more in the case thereexists a band discontinuity is 400 mev or more.

[0278] Thus, there holds a relationship explained with reference toFIGS. 23 and 24 between the Al compositional difference and the valenceband discontinuity, and the valence band discontinuity of 400 meVcorresponds to the Al compositional difference of 0.8 or more. Thus, inthe case the Al compositional difference is 0.8 or more, the thicknessof 30 nm or more is needed for the heterospike buffer layer 18 c so asto reduce the resistance effectively By providing such a heterospikebuffer layer as such, it is possible to reduce the resistance of thedistributed Bragg reflector effectively.

[0279] With regard to the upper limit of the heterospike buffer layer,the thickness of the heterospike buffer layer 18 c is chosen in view ofthe tuned wavelength of the distributed Bragg reflector such that thereoccurs little decrease of reflectance Thereby, it becomes possible torealize a distributed Bragg reflector having excellent characteristicsboth in terms of electric properties and optical properties.

[0280] In the distributed Bragg reflector of the present invention tunedto the design wavelength of 1.1 μm, it is also possible to set thethickness of the heterospike buffer layer 18 c with respect to the tunedwavelength λ [nm] to be equal to or smaller than (50λ−15) [nm]. In sucha case, too, it is possible to reduce the resistance of the distributedBragg reflector while maintaining high reflectance. FIG. 25 shows therelationship between the thickness of the heterospike buffer layer andreflectance of the distributed Bragg reflector tuned to the wavelengthof 1.1-1.7 μm. It should be noted that the distributed Bragg reflectorhas a structure explained with reference to FIG. 3 and uses GaAs for thehigh refractive index layer 18 b and AlAs for the low refractive indexlayer 18 a. The layers 18 a and 18 b are repeated with the numberdetermined such that the reflectance exceeds 99.9% at each of the tunedwavelengths. Thus, in the case of the reflector is tuned to 0.88 μm, thelayers 18 a and 18 b are repeated 18 times, while in the case of thereflector is tuned to 1.1 μm, the layers 18 a and 18 b are repeated 22times. Further, in the case the reflector is tuned 1.3 micron, thelayers 18 a and 18 b are repeated 23 times while in the case thereflector is tuned to 1.5 μm, the layers 18 a and 18 b are repeated 23times. Further, in the case the reflector is tuned to 1.7 μm, the layers18 a and 18 b are tuned to 24 times.

[0281]FIG. 26 shows a change rate of the resistivity of the distributedBragg reflector shown in FIG. 25 (dR/dt) with the thickness of theheterospike buffer layer.

[0282] From FIG. 25, it can be seen that reflectance of the reflectordecreases with increasing thickness of the heterospike buffer layer.Further, FIG. 26 shows that the decrease of the reflectance increasessuddenly at a certain thickness of the heterospike buffer layer. For thesake of facilitating understanding of this situation, FIG. 26 showslines drawn as a tangential for each of the curves as the referencereflectance change rate. For example, in the distributed Bragg reflectortuned to 1.3 μm, it can be seen from FIG. 26 that the change rate of thereflectance increases sharply when the thickness of the heterospikebuffer layer 18c has exceeded 50 nm. In correspondence thereto, thereoccurs a sharp drop in the reflectance of the distributed Braggreflector. Thus, in the surface-emission laser diode having such adistributed Bragg reflector for the reflector, the threshold current oflaser oscillation increases sharply at the foregoing thickness of theheterospike buffer layer 18 c Further, it should be noted that thethickness of the heterospike buffer layer 18 c corresponding to such asharp change of reflectance changes depending on the design wavelengthof the laser diode. Thus, longer the design wavelength of the laserdiode, the thickness of the semiconductor layers constituting thereflector is increased, and the effect of the heterospike buffer layeris reduced.

[0283] Thus, the thickness of the heterospike buffer layer correspondingto such a sudden increase of change rate of the reflectance changeddepending on the design wavelength, while the threshold of the changerate corresponding to the onset of the sudden growth does not changewith the design wavelength and maintains the value of about 0.9 as canbe seen from FIG. 26.

[0284] Table 2 below summarizes the threshold thickness for eachwavelength shown in FIG. 25. TABLE 2 design wavelength 1.1 μm 1.3 μm 1.5μm 1.7 μm threshold thickness  40 nm  50 nm  60 nm  70 nm

[0285] From Table 2, it can be seen that the design wavelength and thethreshold thickness are in a generally linear relationship and thereholds a relationship between the threshold thickness t [nm] and thedesign wavelength [nm] of the distributed Bragg reflector as follows:

t=50λ−15  (1)

[0286] Thus, by providing the heterospike buffer layer 18 c in thedistributed Bragg reflector tuned to the wavelength of 1.1 μm or morewith the thickness not exceeding the thickness t given by Equation (1),it is possible to realize a low-resistance distributed Bragg reflectorhaving a high reflectance.

[0287] In the example above, it was assumed that the heterospike bufferlayer has a linear compositional graduation profile. However, it is alsopossible to use non-linear profile. In this case, too, similar resultsand effects are achieved.

[0288] In the present invention, it is possible to increase thethickness of the heterospike buffer layer to be 20 nm or more in thedistributed Bragg reflector having a thickness of 1.1 μm. In this case,too, it is possible to reduce the resistance of the mirror whilemaintaining a high reflectance.

[0289] As explained before, there holds a relationship of Equation (1)between the thickness of the heterospike buffer layer and the designwavelength of the distributed Bragg reflector that can maintain a highreflectance.

[0290] With regard to the electric properties of the distributed Braggreflector, it is possible to reduce the effect of the hetero interfaceby increasing the thickness of the heterospike buffer layer as notedbefore, and a distributed Bragg reflector having a reduced resistance isobtained. Further, the effect of the resistance reduction by theheterospike buffer layer id determined by the materials used for thedistributed Bragg reflector and the doping density and further by thecompositional profile. Essentially, it does not depend on the reflectionwavelength. Thus, it is concluded that there exists a lower limit in thethickness of the heterospike buffer layer in which the resistance of thedistributed Bragg reflector is decreased sufficiently. In order toprovide a distributed Bragg reflector having a sufficiently lowresistance, it is necessary to provide the heterospike buffer layer witha thickness exceeding a predetermined thickness.

[0291] In the example of the distributed Bragg reflector of FIG. 24 inwhich the semiconductor layers are doped uniformly to the doping densityof 1×10¹⁸ cm⁻³, it can be seen that the resistivity of the distributedBragg reflector increases in terms of orders when the thickness of thedistributed Bragg reflector is les than 20 nm. When the thickness of theheterospike buffer layer has exceeded the value of 20 nm, on the otherhand, it is preferable to use the thickness of 20 nm or more for theheterospike buffer layer, provided that the semiconductor layersconstituting the distributed Bragg reflector has the foregoing doingdensity.

[0292] From the description noted above, it is concludes that adistributed Bragg reflector having a sufficiently low resistance andsimultaneously maintaining a high optical reflectance is obtained bychoosing the thickness t [nm] of the heterospike buffer layer withregard to the design wavelength λ of the distributed Bragg reflector soas to satisfy the relationship 20≦t≦50λ−15.

[0293] In the distributed Bragg reflector of this embodiment, it is alsopossible to set the thickness of the heterospike buffer layer to be 30nm or more. Even in such a case, it is possible to decrease theresistance of the reflector effectively while maintaining a highreflectance at the tuned wavelength or design wavelength of 1 μm orlonger.

[0294] In semiconductor materials, there is a tendency that opticalabsorption increases also for the photons having energy smaller than thebandgap with increase of free carriers. Further, in the case of thep-type semiconductor materials, there arises conspicuous opticalabsorption caused as a result of the valence band to valence bandabsorption with the increase holes acting as the carriers. As theproblem of the valence band to valence band absorption becomesconspicuous with increasing optical wavelength, this problem becomes aserious problem in the distributed Bragg reflector having a longwavelength of 1.1 μm or more. It should be noted that such opticalabsorption becomes the cause of decreasing the reflectance of thedistributed Bragg reflector. In the case of the laser diode using such areflector, there arises a problem of increase of threshold currentcaused by optical absorption and decrease of efficiency. Thus, from theview point of decreasing the optical absorption, it is preferable thatthe doping density of the semiconductor layers is set as small aspossible. However, with the decrease of the doping density, there arisesa problem of increase of thickness of the heterointerface, and theeffect of the interface potential is increased, thus leasing to theproblem of increase of resistance of the distributed Bragg reflector.

[0295] Thus, in the case of the semiconductor distributed Braggreflector having the reduced doping density, it is necessary to use athicker heterospike buffer layer for reducing the resistivity. In thecase of doping the semiconductor layers constituting the distributedBragg reflector to the doping density of 5×10¹⁷ cm⁻³, it can be seenfrom FIG. 23 that the resistivity is reduced to the level of the bulkmaterial when the thickness of the heterospike buffer layer is increasedto 30 nm or more.

[0296] With regard to the doping density and profile, there are numerouscombinations, while there arises a similar tendency when the dopingdensity of one of the semiconductor layers is less than 1×10¹⁸ cm⁻³.This is because the potential barrier formed at the hetero interface hasthe height and thickness depending on the doping density of thesemiconductor layer adjacent to the hetero interface. Lower the dopingdensity, as in the case of the doping density having a value of 1×10¹⁸cm⁻³, larger the influence of the hetero interface. Further, theelectric property of the distributed Bragg reflector is mainlydetermined by the hetero interface where the doping density is small.Thus, the present invention is effective also in the case in which atleast one of the semiconductor layers constituting the distributed Braggreflector has a doping density of less than 1×10¹⁸ cm⁻³.

[0297] It should be noted that a similar tendency appears also in thecase of the distributed Bragg reflector doped to the order of 1×10¹⁷cm⁻³. Of course, it is possible to reduce the doping density further,provided that the thickness of the heterospike buffer layer is increasedto 30 nm or more within the upper limit noted before.

[0298] Thus, according to the present embodiment, it is possible toobtain a distributed Bragg reflector having a sufficiently lowresistance and high optical reflectance by choosing the thickness t [nm]of the heterospike buffer layer with regard to the design wavelength λof the laser diode so as to fall in the range of 30≦t≦50λ−15.

[0299] In the conventional laser diode operable at the wavelength bandof 0.85 ìm, there has been a study to provide a heterospike buffer layeras noted above On the other hand, such a heterospike buffer layer ismost effectively used in the long-wavelength surface-emission laserdiode operable at the wavelength of 1.1-1.7 ìm. In the 1.1-1.7 ìm band,for example, it is possible to set the thickness of the material layerconstituting the heterospike buffer layer about twice the thickness forthe case of the 0.85 ìm band, in order to obtain the same reflectance(99.5% or more, for example). Thereby, the resistance of thesemiconductor Bragg reflector is reduced, and the operational voltage,oscillation threshold current, and the like, are likewise reduced.Thereby, advantageous features such as suppression of heating, stablelaser oscillation and low energy drive is obtained for the laser diode.

[0300] Thus, the provision of such a heterospike buffer layer to thesemiconductor Bragg reflector according to the present invention isdeemed an advantageous improvement especially in the case of thelong-wavelength surface-emission laser diode operable in the laseroscillation wavelength of 1.1-1.7 ìm.

[0301] For example, in the case of the surface-emission laser diodeoperable at the wavelength band of 1.3 μm and having a semiconductorBragg reflector in which a low refractive index layer of AlxGa1-xAs(x=1.0) and a high refractive index layer of AlyGa1-yAs (y=0) arestacked for 20 periods, a reflectance of 99.7% or less is obtained,provided that the thickness of the heterospike buffer layer AlzGa1-zAs(0≦y<z<x≦1) is set to 30 nm. Further, a reflectance of 99.5% or more isobtained when the heterospike buffer layer has a thickness of 53 nm.Thus, a film thickness control of ±2% is sufficient when the distributedBragg reflector is designed to have a reflectance of 99.5% or more Inthe experiments, distributed Bragg reflectors were produced with thethickness of 10 nm, 20 nm and 30 nm for the heterospike buffer layer. Itturned out that a reflectance sufficient for practical use was achievedin any of these experiments. In this way, a 1.3 μm band surface-emissionlaser diode having a reduced resistance for the semiconductor Braggreflector was realized and laser oscillation was achieved. The remainingstructural feature of the laser diode thus produced will be explainedlater.

[0302] In a multilayer reflector, there exists a band of highreflectance in the designed wavelength band (assuming that complete filmthickness control is achieved). This is called high reflectance band,wherein the high reflection band may include also the wavelength band inwhich a reflectance exceeding a target value is achieved for a targetwavelength. In the high reflectance band, the reflectance becomeslargest at the designed wavelength, while the reflectance falls off butonly slightly as the deviates from the designed wavelength. When thedeviation exceeds a certain limit, the reflectance falls off sharply.

[0303] Thus, in a multilayer reflector, it is necessary to control thethickness of the multilayer reflector completely with atomic layer levelso that a reflectance exceeding the necessary reflectance is thatachieved at the target wavelength. In practicer a deviation of about ±1%is inevitable for the film thickness, and thus, it is a common placethat the target wavelength and the wavelength in which the reflectanceis maximized are different. In the case the target wavelength is 1.3 μm,for example, the wavelength providing the maximum reflectance isdeviated by 13 μm when there is an error of ±1% in the film thicknesscontrol. Therefore, it is desirable that this high reflectance band hasa wide bandwidth. Here the high reflectance band is defined as thewavelength band in which a reflectance exceeding a necessary reflectanceis obtained for a target wavelength.

[0304] Thus, in the long-wavelength surface-emission laser diodeoscillating at the wavelength of 1.1-1.7 ìm, it is possible to reducethe resistance value of the semiconductor Bragg reflector whilemaintaining high reflectance, by optimizing the constitution of thereflector. Thereby, the operating voltage, oscillation thresholdcurrent, and the like, of the laser diode are successfully reduced, andheat generation is suppressed effectively. As a result, stable laseroscillation is realized and low energy driving of the laser diodebecomes possible.

[0305] Once again FIG. 1 is referred to.

[0306] It can be seen that a p-type GaAs layer 19 having a compositionrepresented as AlxGa1-xAs (x=0) is provided on the upper semiconductorBragg reflector 18 as a contact layer (p-contact layer), so as toachieve a contact with the p-side electrode 20.

[0307] In the constitution of FIG. 1, it should be noted that the Incontent x of the quantum well active layer is set to 39% (Ga0.61In0.39As). Further, the thickness of the quantum well active layeris set to 7 nm. The quantum well active layer thus formed accumulates acompressional strain of about 2.8% with respect to the G s substrate.

[0308] In the surface-emission laser diode of FIG. 1, the deposition ofthe semiconductor layers is conducted by an MOCVO process. In this case,no lattice-relaxation phenomenon was observed. Each of the semiconductorlayers of the laser diode may be formed by using TMA (trimethylaluminum), TMG (trimethyl gallium) TMI (trimethyl indium), AsH₃(arsine), PH₃ (phosphine) as source materials, together with a carriergas of H₂. In the case of growing the active layer (the quantum wellactive layer) in the form of highly strained layer as in the case of thedevice of FIG. 1, it is preferable to use a low temperature growthprocess that realizes a non-equilibrium growth. In the present case, theGaInAs layer 15 a (quantum well active layer) is grown at 550° C. Itshould be noted that the MOCVD process used herein is characterized byhigh degree of supersaturation and is suited for the crystal growth ofhighly strained active layer. Further, the MOCVD process does notrequire high vacuum environment as in the case of MBE process. Further,the MOCVD process is suitable for mass production, as the processcontrol is achieved by merely controlling the supply rate or supplyduration of the source gases.

[0309] In the illustrated laser diode, there is formed a high resistanceregion 15F outside the current path by means of ion implantation ofprotons (H+) as a current confinement structure.

[0310] In the constitution of FIG. 1, it should be noted that there isformed a p-side electrode 20 on the p-type contact layer formed in turnon the uppermost part of upper part reflector 18 and constituting a partthereof, except for an optical exit part 20A. Also there is formed ann-side electrode 21 at the rear surface of the substrate.

[0311] In the present embodiment, it should be noted that the activeregion including the upper part and lower part spacer layers 14 and 16in addition to the multiple quantum well active layer 15 and forming theresonator between the upper and lower reflectors 12 and 18, in which thecareer recombination is caused upon injection of carriers, is formed ofa material not containing Al (the proportion to the group III element(s)is 1% or more). Furthermore the low refractive index layers constitutingthe lower is part reflector 12 and also the upper part reflector 18closest to the active layer is formed of the non-optical recombinationelimination layers 13 and 17 each having a composition ofGaxIn1-xPyAs1-y (0<x≦1,0<y≦1), in which the compositional parameters xand y are chosen appropriately. More specifically, GaInP or GaInPAs orGaPAs is used for the non-optical recombination elimination layer. Thematerial constituting the non-optical recombination elimination layerthus has a composition of GaxIn1-xPyAs1-y (0<x≦1,0<y≦1), wherein thenon-optical recombination layer may be added further with a trace amountof element(s) other than Al.

[0312] In such a structure, the careers are confined between the lowrefractive index layer of the upper part reflector and the lowrefractive index layer of the lower part reflector that are locatednearest to the active layer and formed of a wide gap material In such astructure, there occurs non-optical recombination of carriers even whenthe active region is formed of the layer not containing Al (theproportion of Al with regard to group III elements is 1% or less) uponinjection of the careers, as there occurs non-optical recombination ofcarriers at the interface between the active layer and the lowrefractive index layer of the upper or lower reflector, as long as theforegoing low refractive index layer (wide gap layer) contains Al. Whenthe non-optical recombination of carriers takes place, the efficiency ofoptical emission is deteriorated. Therefore it is desirable to form notonly the active region but also the low refractive index layersadjoining thereto by a material not containing Al.

[0313] Further, the non-optical recombination elimination layer havingthe primary composition of GaxIn1-xPyAs1-y (0<x≦1,0<y≦1) has a latticeconstant smaller than the lattice constant of the GaAs substrate. Thus,the layer accumulates a tensile strain.

[0314] In an epitaxial growth process, the growth is made whilereflecting the information of the foundation layer on which the growthis made. Thus, when there are defects on surface of the foundationlayer, the same defects crawl up to the growth layer. On the other hand,it is known that such a crawling up of the defects can be suppressed byinterposing a strained layer on the path of the defects.

[0315] In the case an active layer accumulates therein a strain, theresometimes occurs a problem in that growth of the active layer withdesired thickness is difficult because of the reduced criticalthickness. Particularly, there arises a problem in that the film growthdoes not take place at all even if a low temperature growth process ornon-equilibrium growth process is employed, due to the existence ofdefects. This problem occurs particularly when the active layeraccumulates a compressive strain of 2% or more, or when growing theactive layer beyond the critical thickness thereof.

[0316] On the other hand, when there exists a strained layer adjacent tothe active layer, such a crawling up of the defects is intercepted andthe efficiency of optical emission is improved. Further, it becomespossible to grow the active layer even in the case the active layeraccumulates a compressive strain of 2% or more. Further, it is possibleto grow the strained layer beyond the critical thickness.

[0317] It should be noted that the GaxIn1-xPyAs1-y (0<x≦1,0<y≦1) layers13 and 17 adjoin the active region and function so as to confine thecareers into the active region. On the other hand, the GaxIn1-xPyAs1-y(0<x≦1,0<y≦1) layers 13 and 17 also have the feature in that the bandgapenergy can be increased by decreasing the lattice constant. In the caseof GaxIn1-xP (y=1), for example, there occurs an increase of the latticeconstant when the compositional parameter x has increased and the filmcomposition has approached the composition GaP. Associated therewith,there occurs an increase of bandgap. It should be noted that the bandgapenergy Eg is given as Eg (Γ)-1.351+0.643x+0.786x² in the case of directtransition and Eg (X)=2.24+0.02x in the case of indirect transition.Therefore, the hetero barrier height between the active region and theGaxIn1-xPyAs1-y (0<x≦1,0<y≦1) layer 13 or 17 is increased and the degreeof career confinement is improved. Thereby, the threshold current isreduced and the temperature characteristics are improved.

[0318] Furthermore, it should be noted that the non-opticalrecombination elimination layer 13 or 17 having the compositionGaxIn1-xPyAs1 (0<x≦1,0<y≦1) has a lattice constant larger than thelattice constant of the GaAs substrate. Also the lattice constant of theactive layer is larger than the lattice constant of the GaxIn1-xPyAs1(0<x≦1,0<y≦1) layer 13 or 17. Thus, these layers accumulatecompressional strain therein. As the direction of the strain accumulatedin the GaxIn1-xPyAs1-y (0<x≦1,0<y≦1) layer is the same as the directionof the strain accumulated in the active layer, the substantial amount ofthe compressional strain that the active layer senses is reduced. Largerthe strain, the influence of external factor is also large. Thus, theconstruction of the present invention is especially effective in thecase that the active layer accumulates a large compressional strain of2% or more, or the critical film thickness has been exceeded.

[0319] It is preferable to form a surface-emission laser diode of the1.3 μm band on a GaAs substrate. Further, there are many cases in whicha semiconductor multilayer reflector is used for the resonator In such acase, it is necessary to grow 50 to 80 semiconductor layers with a totalthickness of 5-8 μm. (In the case of an edge-emission type laser diode,on the other hand, the total thickness before growth of the active layeris about 2 μm, and itg is sufficient to grow just about three layers.)

[0320] Thus, even if a high quality GaAs substrate is used, increase ofdefect density of the surface on which the growth of the active layer ismade, in the sate immediately before the growth of the active layergrowth is inevitable. Once formed, the defects thus formed crawl up inthe direction of the crystal growth. Further, there may be additionaldefect formation at the hetero surface. On the other hand, measures suchas provision of strain layer before the growth of the active layer orreduction of the substantial strain which the active layer senses, areeffective for reducing the influence of the defects on the surface onwhich the growth of the active layer is made in the state immediatelybefore the growth of the active layer.

[0321] In this embodiment, Al is expelled from the active layer andfurther from the interface region between the active region and thereflector. Thus, the problem of non-optical recombination of carriersoriginating from the crystal defects and caused by Al at the time ofcareer injection is successfully removed.

[0322] As noted before, while it is preferable to provide thenon-optical recombination elimination layer not containing Al at theinterface of both of the reflectors 12 and 18, beneficial effect can beobtained also in the case the non-optical recombination eliminationlayer is provided to only one of the reflectors. In the illustratedexample, both of the upper and lower reflectors 12 and 18 are formed ofthe semiconductor Bragg reflector. However, it is possible to form oneof the reflectors by the semiconductor Bragg reflector and form theother reflector by a multilayer dielectric reflector.

[0323] In the foregoing example, only the low refractive index layercloset to the active layer forms the GaxIn1-xPyAs1-y (0<x≦1,0<y≦1)non-optical recombination elimination layer 13 or 17 in any of thereflectors 12 and 18. However, it is possible to form the non-opticalrecombination elimination layer 13 or 17 by a plurality of GaxIn1-xPyAs1(0<x≦1,0<y≦1) layers.

[0324] In this embodiment, the above concept is applied particularly tothe lower reflector 12 located between the GaAs substrate and the activelayer, and the problem of crawling up of crystal defects originatingfrom Al at the time of the growth of the active layer and the adversaryinfluence thereof, are suppressed successfully As a result, the activelayer can be grown with high quality, and a highly reliablesurface-emission laser diode oscillating with high efficiency andsufficient for practical use-is obtained. In the present embodiment, theAl-free, GaxIn1-xPyAs1 (0<x≦1,0<y≦1) layer is used only for the lowrefractive index layer located closest to the active region in thesemiconductor Bragg reflector. Therefore, it is possible to achieve theforegoing effect without increasing the number of stacks of thereflector.

[0325] The surface-emission laser diode thus produced oscillatedsuccessfully at the wavelength of about 1.2 μm. While the wavelength ofGaInAs formed on a GaAs substrate increases with increase of In contenttherein, such an increase of the In content is accompanied with anincrease of strain. Thus, it has been thought that the wavelength of 1.1μm would be the limit of the increase of laser oscillation wavelength inthe laser diode that uses GaInAs. See IEEE Photonics. Technol. Lett.Vol.9 (1997) pp.1319-1321.

[0326] In the present invention, the inventor could successfully achievethe laser oscillation at 1.2 μm by using highly non-equilibritim growthprocesses conducted at low temperature of 600° C. or less. By using sucha process, it became possible to achieve a coherent growth of the highlystrained GaInAs quantum well active layer with large thickness notpossible before. Meanwhile, this wavelength is transparent with respectto a Si semiconductor substrate. Thus, the laser diode of the presentinvention can be used to construct a circuit chip that uses opticaltransmission through the Si substrate, by integrating an electronicdevice and an optical device commonly on a Si substrate.

[0327] From the explanation noted above, it was discovered that along-wavelength surface emission laser diode can be constructedsuccessfully on a GaAs substrate by using a highly strained GaInAs layercontaining a large amount of In and hence a large amount of compressivestrain for the active layer.

[0328] As noted before, such a surface-emission laser diode can beformed by using an MOCVD process. However, it is also possible to use anMBE process or other growth process for this purpose. In the embodimentdescribed heretofore, a triple quantum well structure (TOW) was used forthe active layer. However, it is also possible to use a structure havingdifferent number of quantum well layers (SQW, MQW).

[0329] Further, it should be noted that the laser diode may also have adifferent structure. Further, the resonator length is not limited toλbut may have a length of integer multiple of λ/2 or preferably λ.

[0330] In the embodiment described heretofore, the laser diode wasconstructed on the GaAs substrate. However, it is also possible to usean InP substrate. Further, the period of repetition of in the reflectorsmay be changed.

[0331] In the embodiment described heretofore, the active layer ofGaxIn1-xAs (GaInAs active layer) containing Ga, In and As as the majorelement is used in this example. On the other hand, it is possible toadd N to the active layer of the laser diode. In this case, the activelayer contains Ga, In, N and As as major elements (GaInNAs activelayer), and the laser diode can oscillate at further longer wavelengths.

[0332] By changing the composition of the GaInNAs active layer, it ispossible to achieve laser oscillation at any of the 1.3 μm band and 1.55μm band. By choosing the composition of the active layer appropriately,it is also possible to realize a surface-emission laser diode laseroscillating at further longer wavelengths such as 1.7 lm.

[0333] It is also construct a surface-emission laser diode operable atthe wavelength of 1.3 μm band on a GaAs substrate by using GaAsSb forthe active layer.

[0334] Conventionally, there has been no material suitable for realizinga laser diode operable at the wavelength of 1.1-1.7 ìm. By using ahighly strained layer of GaInAs, GaInNAs or GaAsSb for the active layer,and by using a non-optical recombination elimination layer, the presentinvention successfully realized a highly efficient surface-emissionlaser diode operable in the long wavelength region of a/the 1.1-1.7 ìmband.

[0335] [Second Embodiment]

[0336] Next, the constitution of another long-wavelengthsurface-emission laser diode applicable to an opticaltransmission/reception system of this invention as a light-emittingdevice that is will be described by using FIG. 27. In the drawing, thoseparts corresponding to the parts described previously are designated bythe same reference numerals and the description thereof will be omitted.

[0337]FIG. 27 is referred to.

[0338] Similarly to the previous embodiment of FIG. 1, this embodimentalso uses an n-type GaAs substrate 11 having a surface orientation of(100).

[0339] On the GaAs substrate 11, it can be seen that the n-typesemiconductor Bragg reflector (Al_(0.9)Ga_(0.1)As/GaAs lower partreflectors) 12 is formed by alternately depositing the n-type AlGaAshaving a composition of AlxGa1-xAs (x=0.9) and an n-type GaAs having acomposition of AlxGa1-xAs (x=0) alternately for 35 periods, each with athickness of 1/4 times the oscillation wavelength λ in each medium(thickness of λ/4). Further, the n-type InGaP layer 13 is formed on thelower Bragg reflector 12 with a composition of GaxIn1-xPyAs1-y (x=0.5,y=1) and a thickness of 1/4. Thereby, the n-type GaxIn1-xPyAs1-y (x=0.5,y=1) layer 13 forms one of the low refractive index layers constitutinga part of the lower part reflector 12.

[0340] On the InGaP layer 13, the multiple quantum well active layer 15is formed by stacking the undoped lower GaAs spacer layer 14 and furtherthe GaxIn1-xNyAs1-y quantum well active layer 15 a three times on thespacer layer 14, with the GaAs barrier layer 15 b of 15 nm thicknessinterposed therebetween to form a triple quantum wells (TQW) structure.Further, the undoped upper GaAs spacer layer 16 is formed on themultiple quantum well active layer 15 thus formed, wherein the lowerspacer layer 14, the multiple quantum well active layer 15 and the upperGaAs spacer layer 16 constitute together a resonator 15R having athickness of one wavelength (λ) of the oscillation wavelength in themedium. The resonator 15R constitutes the active region of thesurface-emission laser diode.

[0341] Further, the p-type semiconductor Bragg reflector (the upper partreflector) 18 is formed on the resonator 15R.

[0342] It should be noted that the upper part reflector 18 includes alow refractive index layer having a thickness of 3 λ/4 formed of an AlAslayer 18 used for a selective oxidizing layer, wherein the foregoing lowrefractive index layer is sandwiched by the GaInP layer 17 and an AlGaAslayer. The GaInP layer 17 is doped with C has a composition representedas GaxIn1-xPyAs1 (x=0.5, y=1), wherein the GaInP layer 17 is formed tohave a thickness of λ/4-15 nm. On the other hand, the AlAs layerconstituting the selective oxidizing layer is doped with C and has acomposition represented as AlzGa1-zAs (z=1) and a thickness of 30 nm.Further, the foregoing AlGaAs layer is a C-doped AlGaAs layer having acomposition represented by AlxGa1-xAs (x=0.9) and a thickness of 2λ/4-15 nm.

[0343] On the foregoing low refractive index layer, a GaAs layer havinga thickness of λ/4 is formed for one period, and a p-type AlGaAs layer,doped with C and having a composition of expressed with AlxGa1-xAs(x=0.9) and a p-type GaAs layer doped with C and having a compositionrepresented by AlxGa1-xAs (x=0), are stacked 22 periods each with athickness of 1/4 times the laser oscillation wavelength in each medium.Thereby a periodic stack structure constituting the essential part ofthe upper part reflector 18 is formed.

[0344] I this embodiment, too, the heterospike buffer layer 18 c ofintermediate refractive index is provided in the semiconductor Braggreflector 18 by an AlzGa1-zAs (0≦y<z<x≦1) layer between the lowrefractive index layer 18 a and the high refractive index layer 18 b asalready explained with reference to FIG. 2. In FIG. 10, illustration ofthe heterospike buffer layer 18 c will be omitted for the sake ofsimplicity.

[0345] In this embodiment, the p-type GaAs layer having the compositionof AlxGa1-xAs (x=0) and constituting the uppermost part of thesemiconductor Bragg reflector 18 functions as a contact layer (p-contactlayer) that secures electrical contact to the electrode.

[0346] In the surface-emission laser diode of this embodiment, the Incontent x of the quantum well active layer 15 a is set to 37% and the N(nitrogen) content is set to 0.5%. The thickness of the quantum wellactive layer 15 a is set to 7 nm.

[0347] In this embodiment, the growth of the semiconductor layersconstituting the said surface-emission laser diode was conducting byusing an MOCVD process. More specifically, TMA (trimethyl aluminum), TMG(trimethyl gallium), TMI (trimethyl indium), AsH3 (arsine) and PH3(phosphine) are used respectively as the source materials of Al, Ga, In,As and P. Further, DMHy (dimethyl hydrazine) was used as the sourcematerial of nitrogen. DMHy decomposes at a low temperature and is suitedfor a low temperature growth process conducted at 600° C. or less.Particularly, it is suited to grow a quantum well layer of large strain,which needs a low temperature growth process. In the MOCVD process, H₂is used for the carrier gas. Further, the growth of the GaInNAs layer(quantum well active layer) was conducted at 540° C.

[0348] It should be noted that MOCVD process is characterized by largedegree of supersaturation and is suited for the crystal growth of amaterial that contains N and simultaneously other group V elements.Further, the MOCVD process does not require the high vacuum environment,contrary to the MBE process. Further, it is suitable for massproduction, as it is only sufficient to control the supply rate andsupply time of the source gases.

[0349] In this embodiment, a predetermined part of the stacked structurethus formed is etched until it reaches the p-type GaxIn1-xPyAs1 (x=0.5,y=1) layer 17. Thereby, there is formed a mesa structure that exposesthe p-AlzGa1-zAs (z=1) selective oxidizing layer 181 at the sidewallthereof. Furthermore, said AlzGa1-zAs (z=1) layer 18 ₁ thus exposed isoxidized from the mesa sidewall by water vapor, and there is formed acurrent confinement layer 182 having a composition represented as AlxOy.

[0350] Finally, the part removed with the mesa etching processpreviously is filled by polyimide to form a planarized structure, andthe polyimide film covering the upper part reflector is removed. Withthis, there is formed a polyimide region 18 ₃. Furthermore the p-sideelectrode 20 is formed on-the p-type contact layer except for theoptical exit part, and an n-side electrode 21 is formed on the rear sideof the GaAs substrate 11.

[0351] In this embodiment, the GaxIn1-xPyAs1 (0<x≦1,0<y≦1) layer 17 isinserted below the selective oxidizing layer 18 ₁ as a part of the upperpart reflector 18. In the case a wet etching process by using a sulfuricacid etchant is employed in the formation of the mesa structure, theetching stops spontaneously at the GaxIn1-xPyAs1 (0<x≦1,0<y≦1) layer 17,as a material of the GaInPAs system functions as an etching stopperlayer to the etching process of a material of the AlGaAs system. Thus,by using a wet etching process by a sulfuric etchant for the formationof the mesa structure, it is possible to control the height of the mesastructure rigorously.

[0352] Because of this, the homogeneity and reproducibility are improvedsubstantially for the surface-emission laser diodes that are formedsimultaneously on a substrate and the production cost is reduced. Thisfeature is particularly advantageous when producing a laser diode arrayin which a number of surface-emission laser diodes are integrated inone-dimensional or two-dimensional array.

[0353] In the embodiment of FIG. 10, it is noted that the GaxIn1-xPyAs1(0<x≦1,0<y≦1) layer 17 that acts also as an etching stopper layer isprovided on the side of upper part reflector 18. Further, a similarGaInP layer 13 is provided on the lower part reflector 12.

[0354] In this embodiment, too, the active region 15 sandwiched betweenthe upper and lower reflectors 12 and 18 and cause recombination uponinjection of is carriers is formed of a material free from Al. Further,the low refractive index layer of the lower and upper reflectors 12 and18 closest to the active layer 15 is formed of the non-opticalrecombination elimination layer 13 or 17 having a compositionrepresented by GaxIn1-xPyAs1 (0<x≦1, 0<y≦1). Thus, Al is not containedat the interface between the active region 15 and the reflector 12 or18, and the problem of non-optical recombination caused by the crystaldefects, which in turn are caused by Al, is effectively eliminated.

[0355] While such a construction of using an Al-free material at theinterface between the reflector and the active region is preferablyprovided to both of the upper and lower reflectors 12 and 18, theadvantageous effect of the present invention is obtained also in thecase such a construction is used on only one of the upper and lowerreflectors 18 and 12. Further, it is also possible to use asemiconductor Bragg reflector in only one of the reflectors and form theother reflector by a dielectric reflector.

[0356] As the lower part reflector 12 provided between the GaAssubstrate 11 and the active layer 15 is constructed similarly to thecase of FIG. 1 in the present embodiment, the adversary effects ofcrawling up of the crystal defects, originating from Al, into the activelayer is effectively suppressed. Thereby, the active layer 15 can beformed with high quality.

[0357] It should be noted that such a non-optical recombinationelimination layer 13 or 17 constitutes a part of the semiconductor Braggreflector 12 or 18 in any of the constitution of FIG. 1 or 10, and thus,the thickness thereof is set to 1/4 the oscillation wavelength λ asmeasured in the medium (λ/4). It is also possible to provide such anon-optical recombination elimination layer in plural numbers.

[0358] In the example above, the non-optical recombination eliminationlayer 13 or 17 is provided to a part of the semiconductor Braggreflector 12 or 18. On the other hand, it is also possible to providesuch a non-optical recombination elimination layer inside the resonator15. In the case the resonator 15 is formed of the active layer 15consisting of the GaInNAs quantum well layer 15 a and the GaAs barrierlayer 15b, for example, it is possible to use the GaAs layer as thefirst barrier layer and the non-optical recombination elimination layerof GaInPAs, GaAsP or GaInP as the second barrier layer. Thereby, it ispossible to set the thickness of the resonator to one wavelength. Inthis case, because of the large bandgap of the non-optical recombinationelimination layer as compared with the first GaAs barrier layer, theactive region in which carrier injection takes place is substantiallylimited up to the region of the GaAs barrier layer.

[0359] In the case that the process of removing the residual Al sourcematerial or Al reactant, Al compound or Al during the fabricationprocess of the laser diode, it is possible to provide such a processduring the step of forming the non-optical recombination eliminationlayer. Alternatively, the removal of residual Al may be conducted in aprocess of growing a GaAs layer interposed between the process offorming the Al-containing layer and the process of forming thenon-optical recombination elimination layer.

[0360] According to the present embodiment, it becomes possible to forma highly efficient, reliable surface-emission laser diode. Thereby, itis possible to achieve the foregoing advantageous effect of the presentinvention without increasing the number of stacks in the reflector, asthe non-optical recombination elimination layer formed of the Al-freeGaxIn1-xPyAs1 (0<x≦1,0<y≦1) layer is used in only the low refractiveindex layer located closet to the active region in the semiconductorBragg reflector 12 or 18.

[0361] Further, it should be noted that filling of polyimide is easilymade, and thus, it is possible to provide interconnection wiring formingthe p-side electrode, without risking the disconnection of the wiring atthe stepped part. Thereby, the reliability of the device is improvedfurther.

[0362] It was confirmed that the surface-emission laser diode thusproduced oscillates at the laser oscillation wavelength of about 1.3 μm.

[0363] In the present embodiment, it became possible to construct asurface-emission laser diode of long wavelength band on the GaAssubstrate 11 by using a GaInNAs layer containing Ga, In, N and As forthe major element. By forming a current confinement structure byapplying a selective oxidation process to the AlAs layer 18 ₁ to formthe oxide current confinement layer 18 ₂, the threshold current of laseroscillation is reduced effectively. In such a current confinementstructure, formed of the AlAs layer 18 ₁ in which the selectiveoxidation layer 18 ₂ is formed, it is possible to provide the currentconfinement structure close to the active layer, and lateral diffusionof the injected electric current is suppressed effectively. As a resultof use of such a current confinement structure, it becomes possible toconfine the careers effectively into a minute region not exposed to theatmosphere. The foregoing current confinement structure has anotheradvantageous feature in that the Al oxide constituting the layer 182 hasa low refractive index and the efficiency of carrier confinement isincreased further. Thereby, the efficiency of laser oscillation isimproved furthermore and the threshold electric current is reduced.Further, the current confinement structure has an advantageous featurein that formation thereof is made easily and the production cost isreduced.

[0364] From the explanation noted above, the laser diode of FIG. 10oscillates efficiently at the wavelength of 1.3 μm similarly to the caseof FIG. 1. The laser diode of FIG. 10 also has advantageous feature ofsmall power consumption and low production cost.

[0365] The surface-emission laser diode of FIG. can be formed also by anMOCVD process, similarly to the case of FIG. 1. However, it is alsopossible to use an MBE process or other growth process. Further, it ispossible to use nitrogen or a nitrogen compound such as NH3 in anactivated state.

[0366] Furthermore, it is possible to replace the triple quantum wellstructure (TQW) in the active layer 15 with other structure includingdifferent number of quantum wells such as SQW structure, DQW structureor MQW structure. Further, it is possible to use a laser diode ofdifferent structure.

[0367] By adjusting the composition of the GaInNAs active layer 15 a inthe surface-emission laser diode of FIG. 10, it becomes possible torealize a surface-emission laser diode of the 1.55 μm band and furtherthe 1.7 μm band. In the present invention, the GaInNAs active layer maycontain other III-V elements such as Tl, Sb, P, and the like. Further,it is also possible to construct a surface-emission laser diode of 1.3μm band on a GaAs substrate by using GaAsSb for the active layer.

[0368] In the description heretofore, it was assumed that the activelayer contains Ga, In and Ss as the major elements (GaInAs active layer)or Ga, In, N and As as the active layer (GaInNAs active layer). Further,the active layer may be formed of any of GaNAs, GaPN, GaNPAs, GaInNP,GaNAsSb, and GaInNAsSb. The present invention is particularly effectivealso in these cases in which the active layer contains N.

[0369]FIG. 28 shows the room temperature photoluminescence spectrumobtained for the active layer that includes a GaInNAs/GaAs doublequantum well structure formed by a GaInNAs quantum well layer and a GaAsbarrier produced by an MOCVD process. Further, FIG. 29 shows thestructure of the sample used for the measurement.

[0370]FIG. 29 is referred to.

[0371] It can be seen that there are formed a lower part cladding layer202, an intermediate layer 203A, an active layer 204 containing thereinnitrogen, another intermediate layer 203B, and an and an upper partcladding layer 205 consecutively on the GaAs substrate 201.

[0372] Next, FIG. 28 is referred to.

[0373] The curve A shows the result with regard to the sample that usesan AlGaAs layer as the cladding layer 202 and the double quantum wellstructure is formed while interposing a GaAs layer similar to theintermediate layer 203A or 203B between the quantum wells. The curve B,on the other hand, shows the measurement result with regard to thesample that uses a GaInP layer as the cladding layer 202 and the doublequantum well structure is formed continuously while interposing a GaAslayer similar to the intermediate layer 203A or 203B.

[0374] As can be seen in FIG. 28, the photoluminescence intensity of thesample A has fallen off by one-half or more with respect to thephotoluminescence intensity of the sample B. This means that therearises a problem of decrease of photoemission efficiency of the activelayer when the active layer containing nitrogen therein such as GaInNAsis grown continuously on a semiconductor layer that contains Al asconstituent element such as AlGaAs while using a single MOCVD apparatus.Because of this, the threshold current density of the GaInNAs laserdiode formed on an AlGaAs cladding layer is increased by twice or moreas compared with the case in which the same laser diode is formed on anGaInP cladding layer.

[0375] The inventor of this invention conducted through investigation ofthis problem and obtained a knowledge explained below.

[0376]FIG. 30 shows the depth profile of nitrogen and oxygen in thedevice for the case the cladding layers 202 and 205 are formed by anAlGaAs layer, the intermediate layers 203A and 203B are formed of GaAs,and the active layer is formed of the GaInNAs/GaAs double quantum wellstructure and the device is formed by using a single MOCVD apparatus. Itshould be noted that the measurement of FIG. 30 was conducted under themeasurement condition summarized in Table 1 by secondary ion massspectrometry. TABLE 3 first ion specie Cs+ first acceleration voltage 3.0 kV sputter rate  0.5 nm/s measurement area 160 × 256 μm² degree ofvacuum <3E-7Pa polarity of measured ion −

[0377]FIG. 30 is referred to.

[0378] It can be seen that there appear two nitrogen peaks in the activelayer 204 in correspondence to the GaInNAs/GaAs double quantum wellstructure. Further, it is also noted that an oxygen peak is detected inthe active layer 204. On the other hand, the oxygen concentration in theintermediate layers 203A and 203, which are free from N and Al, is lowerin terms of one order as compared with the oxygen concentration in theactive layer 204.

[0379] Further, the depth profile of oxygen measured about the samplehaving a constitution in which the active layer 204 including thereinthe GaInNAs/GaAs double quantum well structure is formed on the claddinglayer of GaInP together with the GaAs intermediate layers 203A and 203B,has revealed that the oxygen concentration in the active layer 204 is inthe background level.

[0380] Thus, it was confirmed experimentally that the problem of oxygenincorporation into the active layer 204 occurs singularly in the case inwhich the laser diode has the nitrogen-containing active layer 204 inthe state that the active layer 204 is separated from the substrate bythe semiconductor layer 202 containing Al and the growth of the layersconstituting the device is conducted by a single MOCVD apparatus whileusing a nitrogen compound source material and an organic Al sourcematerial. The oxygen atoms thus incorporated into the active layer forma non-optical recombination state therein and cause a decrease ofluminous efficacy of the active layer.

[0381] Thus, from the result of FIG. 30, it is concluded that oxygenincorporated into the active layer is the cause the problem of deceaseof optical emission efficiency in the device in which the Al-containinglayer is provided between the substrate and the N-containing activelayer. It is conceivable that the origin of this oxygen contaminationwould be the oxygen-containing material that has captured residualoxygen in the deposition apparatus or the impurity contained in thenitrogen compound source material.

[0382] Next, the mechanism of oxygen incorporation into the active layer204 will be examined.

[0383]FIG. 31 shows the depth profile of Al obtained for the same sampleof FIG. 30. The measurement was conducted by the secondary ion massspectroscopy similarly to the case of FIG. 30 under the measurementcondition shown in Table 2. TABLE 4 first ion specie O2+ firstacceleration voltage 5.5 kv sputter rate 0.3 nm/s measurement area  60μm φ degree of vacuum <3E-7OPa polarity of measured ion +

[0384]FIG. 31 is referred to.

[0385] It can be seen that Al is detected in the active layer 204, whichwas formed without introducing an Al source material. Further, it isnoted that the Al concentration in the GaAs intermediate layer 203A or203B formed adjacent to the Al-containing cladding layer 202 or 205 islower than the Al concentration in the active layer 204 by the order ofone. This indicates that Al in the active layer 204 has caused diffusionfrom the Al-containing cladding layer 202 or 205 and has substituted Gain the active layer 204.

[0386] On the other hand, Al was not detected in the active layer in thecase that the N-containing active layer was grown on a semiconductorlayer free from Al such as GaInP.

[0387] From this, it is concluded that Al detected in the active layer204 originates from residual Al such as residual Al source material orresidual Al reactant or residual Al compound or residual Al remaining inthe growth chamber or gas supply line and has been incorporated into theactive layer as a result of coupling with the nitrogen source compoundor the impurity such as water contained in the nitrogen source compound.Further, it is concluded that the Al incorporation into the N-containingactive layer is inevitable when a semiconductor light emitting devicehaving an Al-containing layer between the substrate and the N-containingactive layer is grown continuously by a single epitaxial apparatus.

[0388] By comparing FIG. 31 with FIG. 30, it is noted further that thetwo oxygen peaks in FIG. corresponding to the double quantum well do notcoincide with the two nitrogen peaks but coincide with the peak profileof Al shown in FIG. 31. This results indicates that oxygen in theGaInNAs quantum well layer has been incorporated into the active layernot with the nitrogen source but with Al in the form coupled withresidual Al that has been incorporated into the quantum well layer.

[0389] More specifically, the residual Al source material or residual Alreactant or residual Al compound or residual Al in the MOCVD chamber isthought to cause a coupling with water contained in the nitrogen sourcecompound or oxygen-containing material remaining in the gas line orreaction chamber and is incorporated into the active layer in the formcoupled with oxygen or water.

[0390] Thus, it was clarified by the inventor of the present inventionthat, in the surface-emission laser diode of a conventional GaAs system,there occurs oxygen incorporation into the active layer and oxygen thusincorporated has caused the problem of decrease of efficiency of opticalemission.

[0391] The foregoing discovery provides a clue to the improvement ofefficacy of the surface-emission laser diode of the GaAs system in thatit is necessary to remove the impurity at least from the part of thedeposition apparatus used for the production of the laser diode and mayhave a chance to make a contact with the nitrogen compound sourcematerial in the deposition chamber or the impurity contained in thenitrogen compound source material.

[0392] Thus, by providing a step of removing the residual Al after thegrowth of the Al-containing layer but before the growth of theN-containing active layer, it becomes possible to reduce theconcentration of Al and oxygen impurity incorporated into the activelayer. By doing so, the concentration of residual Al source material orAl reactant or Al compound or Al concentration is already reduced whenthe nitrogen compound source material is supplied for the growth of theN-containing active layer, and the reaction between the residual Al andthe nitrogen source compound or the impurity contained in the nitrogensource compound is successfully suppressed.

[0393] It is further advantageous to remove the residual Al before theend of the growth of the non-optical recombination layer. By doing so,it is possible to suppress the non-optical recombination of carriers inthe active layer at the time carriers are injected into the active layerby way of current injection.

[0394] For example, it became possible to carry out a continuousoscillation of the surface-emission laser diode of the GaAs system atroom temperature environment by reducing the Al concentration in theN-containing active layer to 1×10¹⁹ cm⁻³ or less. Further, by reducingthe Al concentration in the N-containing active layer to 2×10¹⁸ cm⁻³ orless, optical emission characteristics substantially equal to the casewhen the active layer is grown on an Al-free semiconductor layer isobtained.

[0395] The removal of the residual Al source material or residual Alreactant or residual Al compound or residual Al from the part of thedeposition chamber that may have a chance to make a contact with thenitrogen compound source material or the impurity contained in thenitrogen compound source material, can be advantageously conducted by apurging process that uses a carrier gas as the purge gas. Here, the timeof the purging process is defined as the time after the supply of the Alsource material into the deposition chamber is stopped in correspondenceto completion of the growth of the Al-containing layer but before thestart of supply of the nitrogen compound source material to thedeposition chamber for the start of growth of the N-containingsemiconductor layer. It is also possible to interrupt the growth of theintermediate layer, which is free from any of Al and nitrogen, andconduct a purging process by using the carrier gas as a purging gas. Inthis case, the interruption of the growth process of the intermediatelayer may be achieved after the start of growth of the Al-containinglayer until the midway of the growth of the non-optical recombinationlayer.

[0396]FIG. 15 shows an example of the semiconductor light-emittingdevice formed by providing such a carrier purging process. In FIG. 15,those parts corresponding to the parts described previously aredesignated by the same reference numerals and the description thereofwill be omitted.

[0397] Thus, it can be seen that the Al-containing first semiconductorlayer 202, the first lower part intermediate layer 601, the second lowerpart intermediate layer 602, the N-containing active layer 204, theupper part intermediate layer 203, and the second semiconductor layer205 are stacked consecutively the on substrate 201 in FIG. 15.

[0398] In forming the structure of FIG. 15, the crystal growth iscarried out by an epitaxial growth apparatus by using an organic-metalAl source and an organic nitrogen source material. In the case, thegrowth interruption process is provided before the start of growth ofthe second lower part intermediate layer 602 but after the growth of thefirst lower part intermediate layer 601. During the growth interruptionprocess, the part of the growth chamber that may make a contact with thenitrogen compound source material or the impurity in the nitrogencompound source material is purged by a hydrogen gas used as the carriergas, such that the residual Al source material or residual Al reactantor residual Al compound or residual Al is removed.

[0399]FIG. 16 shows the result of measurement of the depth profile of Alconcentration on a semiconductor light-emitting device in which therehas been provided a growth interruption between the first lower partintermediate layer 601 and the second lower part intermediate layer 602and a purging process was conducted for 60 seconds.

[0400]FIG. 16 is referred to. It can be seen that the Al concentrationin the active layer 204 is reduced to 3×10¹⁷ cm⁻³ or less as a result ofsuch a growth interruption process and purging process. This value of Alconcentration is the same degree as the Al concentration in theintermediate layers 601 and 602.

[0401]FIG. 17 shows the depth profile of nitrogen and oxygen for thedevice of FIG. 15.

[0402]FIG. 17 is referred to. It can be seen that the oxygenconcentration in the active layer 204 is reduced to 1×10¹⁷ cm⁻³, whichis a background level. The oxygen peak appearing in the lower partintermediate layer 601 or 602 in FIG. 17 is interpreted as showingoxygen segregation to the growth interruption interface as a result ofinterruption of growth. Thus, it is preferable to conduct the growthinterruption period after the termination of the growth of thesemiconductor layer containing Al but before the growth termination ofthe non-optical recombination elimination layer, in the case there isprovided a growth interruption and purging process. In the non-opticalrecombination elimination layer, it is possible to increase the bandgapenergy as compared with the quantum well active layer or barrier layer,and the adversary effect of the non-optical recombination caused by theoxygen segregated to the growth interruption interface is effectivelysuppressed when career injection is made into the active layer. Theconstitution that uses the non-optical recombination elimination layerprovides a particularly advantageous effect in the case of using anactive layer containing nitrogen.

[0403] In the semiconductor light-emitting device of FIG. 15, theimpurity concentration level of Al and oxygen in the nitrogen-containingactive layer 204 is reduced successfully by interrupting the growthprocess between the first lower part intermediate layer 601 and thesecond lower part intermediate layer 602 and by conducting a purgingprocess for 60 minutes. In this way, the optical efficacy of the activelayer 204 was effectively improved.

[0404] Further, it is also possible to carry out the Al removal processwhile heating the susceptor during the purging process conducted with acarrier gas. By doing so, the Al source material or reaction productadsorbed on the susceptor or the region near the susceptor iseffectively decoupled and removed. In the case of conducting such aheating of the substrate during the purging process, it is necessary tosupply the group V source gas such as AsH3 or PH3 so as to avoid thermaldecomposition of the uppermost semiconductor layer.

[0405] It is also possible to transport the substrate to a chamberdifferent from the growth chamber when conducting the purging processwith a carrier gas in an MOCVD apparatus. In the case that the substrateis transported to another chamber from the growth chamber, it is notnecessary to keep supplying the group V source gas such as ASH₃ or PH₃to the growth chamber. Thereby, the efficiency of thermal decompositionof the Al reactant deposited on the susceptor or the region surroundingthe susceptor is substantially facilitated and the efficiency of removalof Al is improved.

[0406] Further, it is also possible to carry out the purging processwhile continuing the growth of the intermediate layer. In theconstitution of FIG. 10, for example, the non-optical recombinationelimination layer 13 is provided between the N-containing active layer15 and the reflector 12 formed of the AlGaAs material containing Al.Thereby, the distance between the N-containing active layer 15 and theAl-containing layer is increased, and it is possible to increase theduration of the purging process in the case the purging process isconducted simultaneously to the growth. In such a case, it isadvantageous to decrease the growth rate and increase the purging time.

[0407] Further, it is also possible to carry out the growth of theAl-containing reflector 12 of AlGaAs material and the N-containingactive layer 15 in respective, separate apparatuses. In this case, too,the impurity concentration level of Al or oxygen in the active layer 15can be reduced, by setting the regrowth interface below the non-opticalrecombination elimination layer 13.

[0408] In the case that the surface emission laser diode is producedwith the crystal growth process that does not use an organic-metal Alsource or nitrogen compound source material such as an MBE process,there is no report about the degradation of the optical efficiency inthe semiconductor light-emitting device in which N-containing activelayer is provided on the Al-containing semiconductor layer. In case ofan MOCVD process, on the other hand, degradation of optical efficacy ofthe GaInNAs active layer formed on the Al-containing semiconductor layeris reported.

[0409] In Electron. Lett., 2000, 36 (21), pp. 1776-1777, for example,there is a report that the photoluminescence intensity deterioratesremarkably when a GaInNAs quantum well layer is grown continuously on anAlGaAs cladding layer in the same MOCVD growth chamber, even when anintermediate layer of GaAs is provided on the AlGaAs cladding layer. Inthe foregoing report, the GaInNAs active layer is grown in a MOCVDchamber different from one used for growing the AlGaAs cladding layer soas to improve the photoluminescence intensity.

[0410] Thus, it is believed that the aforementioned problem arises moreor less when growing a crystal layer by an organic-metal Al source and anitrogen compound source, as in the case of an MOCVD process.

[0411] In the MBE process, the crystal growth is carried out under aultra low-pressure environment (high vacuum state) On the other hand, anMOCVD process is conducted under a process pressure of several ten Torrto the atmospheric pressure. Thus, the mean free path of the gaseousmolecules is overwhelmingly short in an MOCVD process as compared withthe MBE process. Because of this, it is conceivable that the source gasmolecules or the carrier gas molecules make a contact with various partsof the gas line, reaction chamber, and the like.

[0412] Thus, in the case of the growth process that uses a relativelyhigh pressure for the reaction chamber or gas line as in the case of theMOCVD process, it becomes possible to eliminate the incorporation ofoxygen into the N-containing active layer, by providing a removal stepfor removing the residual Al source material or Al reactant or Alcompound or Al from the location of the reaction chamber, in which thereaction chamber may make a contact with the nitrogen compound sourcematerial or the impurity contained in the nitrogen compound sourcematerial. Such a removal step should be conducted after the growth ofthe Al-containing semiconductor layer but before the start of growth ofthe N-containing active layer. More preferably, the removal processshould be carried out after the growth of the Al-containingsemiconductor layer but before the end of the growth of the non-opticalrecombination elimination layer.

[0413] For instance, it is possible to evacuate the gas line or thegrowth chamber with a vacuum evacuation process after the growth of theAl-containing semiconductor layer but before the growth of theN-containing active layer. In this case, it is preferable to carry outthe evacuation process in the state that the substrate is heated.

[0414] Also, it is possible to remove the residual Al after the growthof the Al-containing semiconductor layer but before the growth of theN-containing active layer by supplying an etching gas. For example, anorganic compound gas may be used as the etching gas that reacts with theAl-containing residue.

[0415] For example, it is possible to cause a reaction in theAl-containing residue by supplying a DMHy gas, which is one of theorganic compound gases, S at the time of the growth of the active layerfrom a DMHy cylinder. Therefore it is possible to remove theseAl-containing residue by causing a reaction between the Al-containingresidue remaining on the reaction chamber surface, heating zone, or jigsused for supporting the substrate, and the organic compound gas bysupplying the organic compound gas from a gas cylinder, after the growthof the Al-containing semiconductor layer. By a method, too, it ispossible to suppress the incorporation of oxygen is into the activelayer. Particularly, by using the same gas as the gas used for thenitrogen source it is possible to avoid the problem of providing aspecial gas line. This process can be carried out while interrupting thegrowth or growing a dummy layer containing nitrogen such as GaNAs,GaInNAs, GaInNP separately from the growth of the active layer.

[0416] By doing conducting the Al removal process simultaneously to thecrystal growth process, it is possible to reduce the time loss ascompared with the case of interrupting the growth process, and thethroughput of the semiconductor device production is improved.

[0417] By using GaInAs in the active layer of laser diode, it becamepossible to realize a laser diode oscillating at the wavelength of 1.2μm by growing a highly strained GaInAs quantum well active layer byusing a low temperature growth process of 600° C. This wavelength valueis substantially longer than the wavelength of 1.1 μm, which has beenconceived as the upper limit of laser oscillation wavelength.Conventionally, there was no material suitable for the laser diode of1.1-1.7 μm. On the other hand, it became possible to realize a highlyefficient surface-emission laser diode operable in the wavelength bandof 1.1-1.7 μm, by using a highly strained active layer of GaInAs,GaInNAs or GaAsSb together with the use of the non-optical recombinationelimination layer. With this, the possibility of applications to theoptical-fiber telecommunication systems was opened.

[0418] [Third Embodimnt]

[0419] [Third Embodiment]

[0420]FIG. 35 shows a laser diode chip 32 including the long-wavelengthsurface-emission laser diode of FIG. 1 or FIG. 27 explained previously.The example that formed on an n-type GaAs wafer 31 of a surfaceorientation (100) is shown.

[0421]FIG. 35 is referred to.

[0422] It can be seen that a number of laser diode chips 32 are formedon the GaAs wafer, and each of the laser diode chips 32 carries thereonn laser diodes each having a construction explained before. The number nand arrangement thereof are decided according to the use of laser diodechip 32.

[0423]FIG. 36 shows the example of the optical transmission/receptionsystem using the long-wavelength surface-emission laser diode having thelaser oscillation wavelength of 1.1-1.7 μm band. Those parts explainedpreviously are designated by the same numerals and explanation isomitted.

[0424]FIG. 36 is referred to.

[0425] The surface-emission laser diode chip 32 is provided at the Apoint as an optical source such that the emission part 32A of the laserdiode chip 32 makes an optical coupling with the optical fiber 33. Theoptical signal emitted from the emission part 32A of the laser diodechip 32 is injected into the optical fiber 33. The optical signal istransferred in the direction shown with the thick arrow in Figure 36.The end point of the optical fiber 33 is located at the B point. Thephotodiode or other suitable photodetection device 34, which constitutesthe photodetection unit is provided in the B point, and the opticaldetection part 34A thereof is coupled optically to and the optical fiber33. Thus, the optical transmission/reception system is composed.

[0426] In this example, the location B for the photodetection unit andthe location A for the optical source are tied with a straight line bythe optical fiber 33.

[0427]FIG. 37 shows the construction of FIG. schematically.

[0428]FIG. 37 is referred to.

[0429] The black circles A, B in the figure show the location of theoptical source 32 and the photodetection unit 34 respectively. A blackthick line shows the optical fiber 33.

[0430] Conventionally, optical source 32 and photodetection unit 34 areconnected optically with optical fiber 33 that provides the transmissionpath and constitute an optical transmission/reception system. Thetransmission path is formed extending from several tens of meters toseveral tens of kilometers in the optical transmission/reception systemwith the long-wavelength surface-emission laser diode of laseroscillation wavelength 1.1-1.7 μm band of this invention. Thereby, theremay be obstacles between the points A and B.

[0431] For example as for FIG. 38, obstacles 35A and 35B exist betweenthe points A and B. Thus, the point B for the location of thephotodetection unit and the point A for the location of the opticalsource cannot be connected with the transmission path 33 of a straightline. Thus, FIG. 38 shows the example of bending the transmission pathby a right angle.

[0432] When the optical fiber 33 is bent at the point where thetransmission path is bent by a right angle with the same angle as in thecase of FIG. 38, the optical fiber 33 is damaged and stops functioningas a transmission path. It is possible to provide a reflection part inthe bending part of the transmission path so as to deflect the opticalbeam. The use of the reflection part in such a bending part of thetransmission path increases the cost.

[0433] Thus, the present invention proposes an approach to bend theoptical transmission path without providing a reflection part andwithout spoiling the functioning of the optical fiber 33 as atransmission path.

[0434]FIG. 39 shows a third embodiment of this invention. Those partsexplained previously are designated by the same reference numerals andexplanation is omitted.

[0435]FIG. 39 is referred to. Obstacle 35C exists between the A pointand B point. The location B and the location A for the photodetectionunit and the optical source 32, respectively, can not be connected by atransmission path of straight line. However, as shown in thisembodiment, the location B for the photodetection unit 34 and thelocation A for the optical source 32 are connected by bending opticalfiber 33, which composes a transmission path without causing a localangle. Thus, the optical fiber 33 composing the transmission path is notdamaged by the bending, and it is possible to avoid the obstacle 35C.According to the present invention it is possible to construct a fineoptical transmission/reception system even when obstacles must beavoided.

[0436]FIG. 40 is another example according to this invention. In thiscase obstacles 35D, 35E exist between the points A and B. Location B andlocation A of photodetection unit 34 and optical source 32,respectively, can not be connected with a straight line transmissionpath.

[0437] However, by bending the optical fiber 33 of the transmissionpath, without causing a local angle, as shown in this example of thisinvention it is possible to connect the location B for thephotodetection unit and the location A for the optical source As aresult, the transmission path is bent continuously in this example ofthe present invention. It-is not formed step-like and a local angle isnot required.

[0438] Furthermore the above explanation pertains to the opticaltransmission/reception system using the long-wavelength surface-emissionlaser diode with laser oscillation wavelength of 1.1-1.7 μm band tosuitably provide middle to long distance telecommunication systems.According to this invention it is possible to deploy this system insideof a building, for example, even in the case of constructing an opticaltransmission/reception system with a length of several centimeters toseveral meters. Even in this case, the transmission direction of theoptical beam can be changed in all directions without providingreflection part, by bending the optical fiber along the transmissionpath, without causing a local angle therein. According to evaluationsconducted by the inventor of the present invention, there was not anycase wherein the function of a transmission path failed due to theoptical fiber 33 being bent, even in the case that the transmission pathwas bent continuously as indicated in FIG. 40. There was no damage tothe transmission paths such as those shown in FIG. 39 and FIG. 40, aslong as the diameter of the curvature of the transmission path does notexceed 20 cm. To put it differently, the transmission path can bearranged to avoid obstacles such as shown in FIG. 40, even if reflectionpart or the like, that changes the direction is not provided, if thediameter of the transmission path curvature does not exceed 20 cm. Thus,the present invention provides a fine optical transmission/receptionsystem that functions with high reliability at a low cost.

[0439] [Fourth Embodiment]

[0440] Next the fourth embodiment of this invention is explained.

[0441]FIG. 41 shows another example of an optical transmission/receptionsystem using the long-wavelength surface-emission laser diode with laseroscillation wavelength of 1.1-1.7 μm band. Those parts explainedpreviously are designated by the same reference numerals and explanationis omitted.

[0442]FIG. 41 is referred to. In this example the laser diode emissionpart 32A is coupled optically to an optical fiber Fl. The laser beamthat is emitted from the laser diode emission part 32A is transferred inthe direction of the thick arrow in FIG. 41. The laser beam that wastransmitted through the optical fiber Fl is then bent 90 degrees by areflection part R. The laser beam then enters optical fiber F2. Opticalfiber F2 at the end point couples optically to the light detector part34A of the photodetection device 34 such as a photodiode. Thus theoptical transmission/reception system is composed.

[0443] It should be noted that the foregoing description is merely forthe exemplary purpose of the optical transmission/reception system ofthis invention. Thus, only one laser diode emission part 32A is shown inthe present example. However, it also is possible to construct, by usingthe advantageous feature of the long-wavelength surface-emission laserdiode of the present invention, to construct a large capacity opticaltransmission/reception system of the multiple laser array type, in whicha number of laser diodes 32A are formed on one laser diode chip 32A andthe optical transmission/reception system is constructed by using anumber of optical fibers F1 and photodetection devices 34 coupledoptically to the laser diodes 32A.

[0444]FIG. 42 shows another arrangement of the opticaltransmission/reception system of FIG. 41. The opticaltransmission/reception system of FIG. may be a yard, whereas in FIG. 42it is arranged inside a wall of a building. Those parts explainedpreviously are designated by the same reference numeral and explanationis omitted.

[0445]FIG. 42 is referred to.

[0446] A room 42 is defined with a wall 41 by which the building isformed. Within a space 41 A inside the wall 41, a long-wavelengthsurface-emission laser diode chip 32 having laser oscillation wavelengthof the 1.1-1.7 μm band is provided at the A point as an optical source.Further, The photodiode that constitutes the photodetection unit 34 isprovided in the B point. Also the reflection part R is provided in thespace 41A so as to deflect the transmission path between the A point andthe B point. FIG. 42 shows the plan view of the room and the opticaltransmission/reception system merely for the purpose of explanation.Because of this, the room or the wall and the opticaltransmission/reception system are not drawn to scale.

[0447] Furthermore, though not indicated by FIG. 42, in each opticaltransmission/reception unit 32 and 34 at the points A and B, there maybeother connect instruments or connectors. These may be in the internalspace 41A of the wall 41, or may be in the room 42.

[0448]FIG. 43 shows the plan view of an optical transmission/receptionsystem in the room 42. Those parts explained previously are designatedby the same reference numerals and explanation is omitted.

[0449]FIG. 43 is referred to. The laser diode 32 and the photodiode 34are tied with one straight line by the optical fiber F12 crossing theinside of room 42. Therefore the optical transmission/reception systemis arranged on the floor, under the floor, or in the ceiling of theroom.

[0450]FIG. 44 shows another example of the opticaltransmission/reception system in the room 42. Those parts explainedpreviously are designated by the same reference numerals and explanationis omitted FIG. 44 is referred to.

[0451] In this case the laser diode 32 and the photodiode 34 are tied bythe optical fiber F12 by curving the optical fiber F12 while utilizingthe flexibility of the optical fiber.

[0452] However, the optical fiber F12 has to be arranged so as to crossthe room 42, but it can change the direction of the transmission pathonly with big curvature even if it uses the flexibility of opticalfiber. However, the optical fiber has to be bent with a large radius ofcurvature, and the optical transmission/reception system has to beconstructed to or under the floor or in the ceiling of room 42 in thestate that the optical fiber 12 crosses the room 42. Thus, it isnecessary to dispose the optical fiber under the floor or on the flooror on the ceiling.

[0453] In the arrangement shown in FIGS. 26 and the optical fiber has tobe arranged so as to cross the room 42. Therefore, the optical fiber onthe floor, under the floor or in the ceiling of the room is arranged ina very complicated and disorderly manner. It gets more complicated whena plural optical transmission/reception system is arranged. Then thereare the problems of intertwisting, and maintenance after installationbecome difficult. Especially, such an arrangement is very dangerous inthe case the optical fiber F12 is arranged on the floor where apedestrian can hook the foot The optical fiber transmission path of thisembodiment of the present invention is well-suited to the wall 41 orpillar or other parts of the building, because the optical fibertransmission path can be bent 90 degrees by using the reflection part Ras shown in FIG. 42 and is otherwise arranged beautifully in appearance,even if it is arranged in a place where it is not inside of wall 41 andcan be seen by the eye. It gets complicated if a plural opticaltransmission/reception system is arranged, but there is not a problem ofthe optical fibers intertwisting. The maintenance after installation canbe done easily.

[0454] The reflection part R for the deflection of the transmission pathis provided, in constructing such a peripheral (out of sight) opticaltransmission/reception system in this embodiment. By using thereflection part R, the transmission path is able to be arrangedeffectively. Instead of exposing the transmission path unnecessarily,the reflection part material R puts the transmission path inside theceiling, under the floor or in the wall of a building. The transmissionpath does not occupy area needlessly. The building design comes to beproduced effectively. The degree of freedom for an aesthetic designincreases.

[0455] Furthermore the reflection part R is not necessarily restrictedto 90 degrees, in the case that the direction of the transmission pathis bent by reflection part material R. However, in the normal case, abuilding is executed/designed, unless there is a demand for a specialdesign, for pillars, walls, floors, and ceilings to provide many caseswhere one straight line crosses another straight line at 90 degrees. Insuch normal cases it is desirable for reasons of esthetic beauty and ofefficiency, when the optical fiber transmission path changes 90 degrees,for it to be arranged along a pillar, wall, floor, ceiling and theothers.

[0456] Also, exposing the optical fiber transmission path to the eyeunnecessarily be avoided in constructing such an opticaltransmission/reception system, by using the reflection part material Rfor changes in direction of the transmission path so that thetransmission path does not occupy area needlessly inside the ceiling,under the floor or in the wall of a building. Thereby the buildingdesign comes to be produced effectively and the degree of freedom foraesthetic design increases.

[0457]FIG. 45 shows an example of another optical transmission/receptionsystem of this embodiment. The optical signal emitting from the emissionpart 32 A of the laser diode 32, in this example, is transferred inspace. It goes straight along the arrow of FIG. 45. It is received withthe light detector part 34 A comprised of a photodiode and otherphotodetection devices 34.

[0458] As explained according to the embodiments of the presentinvention previously, it is preferable to use a surface-emission laserdiode equipped with the improved semiconductor Bragg reflectors 12 and18 further with the non-optical recombination elimination layer andhaving the laser oscillation wavelength band of 1.1-1.7 μm for the laserdiode, in view point of reliability, low power driving, and lowproduction cost. The foregoing wavelength was not possible before in asurface emission laser diode.

[0459] The following description will be made for the construction inwhich there is only one laser diode. However, it should be noted that,in the case of the long-wavelength surface-emission laser diode of the1.1-1.7 μm band, a number of laser diodes are formed on a single chipwith low cost, and it is easy to construct a multiple laser arraysystem. Thereby, a large capacity telecommunication system us realized.

[0460]FIG. 46 is another example of the optical transmission/receptionsystem of this embodiment. Those parts explained previously aredesignated by the same reference numerals and explanation is omitted.

[0461]FIG. 46 is referred to.

[0462] The optical signal emitted from the emission part 32A of laserdiode 32 is transferred through space. It goes straight in the directionof the arrow in FIG. 46. The progress direction of the optical path isbent by a midway, for example by the reflection part R. The opticalsignal is received with the light detector part 34A comprising thephotodetection devices 34 such as a photodiode, and the like.

[0463] [Fifth Embodiment]

[0464] Conventionally the signal transmission of inside an electronicapparatus has been achieved by using a conductor cable in the form ofelectrical signals. Therefore numerous conductor cables are connectedinside various electronic apparatuses. The arrangement/processing of theconductor cable was complicated, presenting problems in the design stageand with the assembling stage at the factory.

[0465] Thereupon, instead of exchanging of the signals by such conductorcable, in this embodiment of this invention the electrical signals aresubstituted for with optical signals by the opticaltransmission/reception system as shown in FIG. 45 or FIG. 46. Theoptical signal that is substituted is transferred through space. Suchsubstitution omits or decreases conductor cable. The conductor cableinside the instrument is decreased as much as possible. Internal wiringis simplified. By simplifying the internal wiring of the electronicapparatus the complexity of the layout and processing of conductor cableis reduced. Reducing or eliminating the complexity can increase thedegree of freedom of each part/unit and other layout items inside theapparatus.

[0466] Electronic apparatuses for which the opticaltransmission/reception system of this embodiment of this invention isincorporated include, for example, recording apparatuses such as acopying machine or laser printer that uses electrophotography, ink-jetrecording apparatus, or recording apparatus using a silver saltphotography process. In addition, the present invention can be used incomputers, video apparatuses, television sets.

[0467] As for FIG. 47, the figure shows an electrophotographic copyingmachine 541 to which this embodiment is applied. FIG. 48 enlarges FIG.47.

[0468]FIG. 48 shows the internal structure of the electrophotographiccopying machine 541 schematically. Those parts explained previously aredesignated by the same reference numerals and explanation is omitted.

[0469]FIGS. 47 and 48 are referred to.

[0470] The electrophotography copying machine 541 has a sheet feedcassette 542 and a sheet recovery tray 543. Furthermore wiring board 550and image formation mechanism 549 including sheet feed mechanism 548 andphotosensitive drum 546 are connected by electrical circuit and includedin the main body case that is closed with cover 547 a and fitted to thecase 547.

[0471] And also the photodiode 34 and the laser diode 32 are located inthe case 547 respectively at the point A and the point B, all previouslyexplained.

[0472] The laser diode 32 and photodiode 34 are connected optically, bythe construction explained with FIG. previously and use optical fiberF1, the mirror R and optical fiber F2

[0473]FIG. 49 shows an ink-jet recording apparatus 551, as anotherexample to which the present invention is suitably applied. FIG. 50 isthe figure that enlarges FIG. 49 and schematically shows the internalstructure.

[0474]FIGS. 49 and 50 are referred to.

[0475] The ink-jet recording apparatus 551 has a case 554 comprising alower part case 554 b and an upper part case 554 a. A sheet feedmechanism 555 and is an ink-jet recording head 556 are provided on theupper part case 554 a.

[0476]FIG. 50 is referred to. The ink-jet recording head 556 is providedso as to move right and left on a carriage 556A. Image formation isperformed on the recording sheet that is pressed on platen roller 558 byrecording part 557.

[0477] Wiring board 559 provides an electronic circuit in the lower partcase 554 b. Optical fiber F12 similar to the embodiment explained aboveis provided between the A point and B point in the wiring board 559.Optical fiber 12 transfers the optical signal to the photodetectiondevice 34 at the B point from the optical source of the laser diode chip32 provided at the A point.

[0478] According to this embodiment of the present invention, conductorcable in the electronic apparatuses is eliminated or reduced. Conductorcable is replaced inside the instrument by an opticaltransmission/reception system. The examples of an electrophotographycopying machine and ink-jet recording apparatus were shown in FIGS.47-50, as the electronic apparatuses to which this embodiment isapplied. This invention is not restricted to these apparatuses.

[0479] [Sixth Embodiment]

[0480] In the recording apparatuses such as an ink-jet recordingapparatuses or recording apparatus of silver salt photography or anelectrophotographic recording apparatus, there arises a problem in thattoners Or ink or liquid developer form a mist. Further, dust particlessuch as paper dust may float inside the apparatus. Thus, the inside ofsuch apparatuses is not an ideal environment for an opticaltransmission/reception system of this invention.

[0481] In consideration this problem, the sixth embodiment of thisinvention shown in FIG. 51 provides a cover member 32B covering thelaser diode chip 32 or a cover member 34B covering the photodiode 34.For example, these cover members 32B and 34B are formed by a transparentglass-like member. In FIG. 51, those parts explained previously aredesignated by the same reference numbers, and explanation thereof willbe omitted.

[0482] It is possible to use a high-precision plastic member, from whichstrain is removed, in addition to a glass, for the cover members 32B and34B. Such a cover member provides physical and chemical protection ofthe laser diode and the photodetection device used in this inventionthat are produced by a sophisticated process.

[0483] Furthermore the toner, ink or paper dust and other foreign mattercannot be allowed to adhere to the laser diode chip of this inventionand spoil the function of the optical transmission/reception system,such as shading of the laser beam. Therefore it is desirable to formthese cover members detachable. By making the cover members detachable,the cover members may be removed right away anytime that foreign matteradheres. Furthermore a cover is not provided to reflection member R inFIG. 51. As occasion demands a cover can be provided also to thereflection member R.

[0484] Considering the contamination originating from toner and paperdusts, it is thought that it would be more effective to provide such acover member 32B or 34B in the apparatuses such as a printer or copyingmachine than a computer or a video apparatus or a television set.

[0485] [Seventh Embodiment]

[0486]FIG. 52 shows an example another optical transmission/receptionsystem that uses the long-wavelength surface-emission laser diode havingthe laser oscillation wavelength of 1.1-1.7 μm band. Those partsexplained previously are designated with the same reference numerals andexplanation is omitted.

[0487]FIG. 52 is referred to. This embodiment concatenates and connectsplural optical fibers along the optical transmission path in theconstruction of FIG. 36 This embodiment enables an optical transmissionpath of long distance. There are three optical fibers in this example.

[0488] The optical telecommunication system was previously studied withthe wavelength of 0.85 μm. However, the transmission loss of the opticalfiber was large at this wavelength and it was not practical. On theother hand, it has been difficult previously to compose thesurface-emission laser diode oscillating stably at a practical longwavelength band in which the transmission loss becomes minimum in theoptical fiber.

[0489] In accordance with this invention, the surface-emission laserdiode that oscillating at the wavelength band of 1.1-1.7 μm is realizedby improving the semiconductor Bragg reflector 12 or 18 and providingthe non-optical recombination elimination layers 13 and 17. Thus apractical long-wavelength band optical telecommunication system is nowpossible.

[0490] In the illustrated example, the laser beam that emitted from thelaser diode emission part 32A of the long-wavelength surface-emissionlaser diode chip 32 is injected into a first optical fiber FG1 fortransmission, and the laser beam exited the first optical fiber FG1 isinjected to a second optical fiber FG2 for further transmission.Furthermore, the laser beam that exited this second optical fiber FG2 isinjected into a third optical fiber FG3 for transmission, wherein a thephotodiode chip 34 having the photodetector part 34A is coupled to thethird optical fiber FG3 for detection Thus, the optical fibers FG1, FG2and FG3 are disposed along the transmission path of the laser beam.

[0491] Between the laser diode chip 32 and the first optical fiber FG1,there is provided an optical connection module MG1 for connecting thelaser diode and optical fiber. Similarly, optical connection modulesMG2, MG3 and MG4 are provided between the optical fibers or between theoptical fiber and the photodiode chip for optical coupling.

[0492]FIG. 53 shows the bi-directional optical transmission/receptionsystem that has the construction that provides transmission system FGAcorresponding to the system of the above FIG. 52 and transmission systemFGB inverted to the system of the FIG. 52. For the parts in the FIG. 53that are the same as those explained above with the same referencenumerals, explanation is omitted.

[0493]FIG. 53 is referred to.

[0494] The transmission system FGB includes, from the right to the left,a third optical fiber FR3 transmitting the laser beam emitted from thelaser diode part 32A of the surface-emission laser diode chip 32, asecond first optical fiber FR2 transmitting the laser beam emitted fromthe optical fiber FR3, a first optical fiber FR1 transmitting the laserbeam emitted from the optical fiber FR2, and the light detector part 34Aof the photodiode chip 34 is coupled optically to the first the opticalfiber FR1.

[0495] A connect module MR4 is provided between the laser diode chip 32and the third optical fiber FR3 in the transmission system FGB, whereinthe connect module MR4 couples optically the laser diode chip 32 and theoptical fiber FR3. Similarly, there are provided connect modules MR1,MR2 and MR3 are for optical couplings respectively between the opticalfibers FR3 and FR2, between the optical fibers FR2 and FR1, and betweenthe optical fiber FR2 and the photodiode chip 34.

[0496]FIG. 54 shows an example of parallel optical telecommunicationsystem in which n optical transmission/reception systems each having theconstruction of FIG. 52 are arranged in parallel.

[0497]FIG. 54 is referred to.

[0498] The plural laser emission part 32 A is provided on a laser diodechip 32. Further, first, second and third optical fiber groups MFG1,MFG2 and MFG3 are constructed by a number of optical fibers eachcorresponding to one of the plural optical emission parts 32A. Further,there are provided a number of photodetector parts 34A in the photodiodechip 34 in correspondence to the plural laser emission parts 32A.

[0499] In the present invention, in which the surface-emission laserdiode chip is used, it is easy to provide a number of laser emissionparts 32A on the laser diode chip 32. By providing a number of laseremission parts 32A on the laser diode chip, it becomes possible torealize a large capacity telecommunication system easily.

[0500] Furthermore it is possible to construct a large capacitybi-directional optical transmission/reception system that expands theoptical transmission/reception system of FIG. 54, in accordance with theconstruction of the bi-directional optical transmission/reception systemof FIG. 53 and using the optical fibers of plural groups in parallel,although FIG. 57 does not indicate a bi-directional system.

[0501] [Eighth Embodiment]

[0502] Next another embodiment of this invention will be explained

[0503]FIG. 55 shows the construction of an optical connection module MG1that is used to optically couple the surface-emission laser diode chip32 and the first optical fiber group MFG1 in the left part of FIG. 54.FIG. 55 shows optical connection module MG1 schematically with arectangular dotted line.

[0504] Detailed construction of the optical connection module MG1 willbe explained hereinafter with reference to FIGS. 39-59. Those partsexplained previously are designated by the same reference numerals andexplanation is omitted.

[0505]FIGS. 56 and 57 show the construction of the surface-emissionlaser diode chip 32 and the optical fiber group MFG1 respectively in thestate before they are coupled and the state after they are coupled.

[0506]FIG. 56 is referred to.

[0507] Optical connection module MG1 shown by a rectangular dotted linepart schematically in FIG. is formed of a fiber holder 61 and a fiberholder 62 that holds each of the optical fibers fg1 that constitutes theoptical fiber group FG1. The Fiber holder 62 is inserted into chipholder 61 as shown in FIG. 57 with arrows so as to face each other.Thus, the optical coupling is achieved between each of the laser diodeemission parts 32A and the edge surface of the corresponding opticalfiber fg1. Thereby the desired optical coupling is achieved.

[0508] In the case of this invention, the holders 61 and 62 are providedwith discrimination means such that each of the laser diode emissionpart 32s A and each of the optical fiber fg1 face with each other inone-to-one relationship, without ambiguity in the lateral or verticaldirections. For this purpose, an arrow mark is provided to each of thelaser diode chip holder 61 and the fiber holder 62 in the example of thedrawing. Thereby, optical connection can be performed very efficiently,because of the ability to discriminate the direction of holders 61 and62 correctly and instantaneously at the time of the connection betweenlaser diode chip 32 and optical fiber group FG1, at the time the opticaltransmission/reception system of the present invention is constructed.

[0509] Furthermore, the discrimination means is not restricted to thearrow mark but it is also possible to use a different color.Furthermore, the discrimination means is not necessarily restricted tothe ones that can be visually recognized. It is possible to have adiscrimination means using the tactile sense by utilizing the unevennessand other features of form. It is possible to discriminate the directionof holders 61, 62 briefly even in the case of construction work indarkness or nighttime, in the case that discrimination means able todiscriminate by the tactile sense is used.

[0510]FIGS. 58 and 59 show a different example of the optical connectionmodule MG1 that consists of the combination of laser diode chip holder61 and fiber holder 62.

[0511]FIGS. 58 and 59 are referred to With the case as shown in FIGS. 39and 40 this embodiment provides discrimination means to each of laserdiode chip holder 61 and fiber holder 62 similarly. So that it ispossible to connect and locate both holders accurately, in thisembodiment a flange surface is additionally formed so as to allow theedge part of laser diode chip holder 61 engage the fiber holder 62. Theflange surfaces 61A and 62B are shown in FIG. 58.

[0512] Next is explained another feature of this invention with regardto the discrimination means, the location/connection means shown inFIGS. 56-59, and the optical connection module MG1 that causes coupledlight between the surface-emission laser diode chip and the 1st opticalfiber group. Yet the concept of this invention is not only applied tooptical connection module MG1 that couples optically thesurface-emission laser diode chip and the first optical fiber group MFG1but it is also applied to the optical connection module MG2 so thatconnects the first optical fiber group MFG1 and the second optical fibergroup MFG2 optically.

[0513]FIG. 60 shows an example of optical connection module MG2 thatcouples optically such an optical fiber group to a different opticalfiber group.

[0514]FIG. 60 is referred to.

[0515] In this case, the means for discriminating the direction isprovided on the fiber holders 64 and 65 in the form of arrow mark suchthat that each optical fiber fg1 of the first optical fiber group MFG1couples properly to the corresponding optical fiber fg2 in the secondoptical fiber group MFG2. By providing such discrimination means itbecomes possible to discriminate the a mutual direction instantaneouslyat the time of the connection between the first optical fiber group MFG1and the second optical fiber group MFG2, as the opticaltransmission/reception system is constructed in accordance with thepresent invention.

[0516] Furthermore, FIGS. 39-59 are examples of the discrimination meansand the present invention is not limited to such an arrow mark. Thediscrimination means might well use the difference of color. Thediscrimination means might well be able to use the tactile sense thatsenses the unevenness and others of a certain form. By using thediscrimination means that is able to use the tactile sense, theadvantage is being able to feel the direction of the fiber holder in thecase of working during darkness, or even in the case of performingconstruction work at night.

[0517] In the construction of FIG. 60, not only the discrimination meansis provided to each of the first fiber group holder 64 and the secondfiber group holder 65, but there are formed the flange surfaces on theedge part of the first fiber group holder 64 (A part of FIG. 60) and onthe edge of the second fiber group holder 65 (B part of FIG. 60) suchthat the flange surfaces engage with each other in the state that thereis an optimum optical coupling.

[0518] Furthermore, such discrimination means and thelocation/connection means can be used also in the optical connectionmodule MG3 that couples the second optical fiber group MFG2 and thethird optical fiber group MFG3 optically or in the optical connectionmodule MG4 that couples optically the third optical fiber group MFG3 andthe photodiode chip 34. When the optical transmission/reception systemis constructed according to this invention, the mutual orientation canbe discriminated between the optical fiber groups or between the opticalfiber group and the photodiode chip instantaneously and exactpositioning and optical coupling is achieved.

[0519] [Ninth Embodiment]

[0520] Furthermore, the optical connection module according to anotherembodiment of the present invention is accomplished by using pluraloptical fibers in parallel. It should be noted that the reason it hasbecome possible to construct the large-capacity opticaltransmission/reception system for a distance from several centimeters toseveral hundred kilometers is that stable laser oscillation ofsurface-emission laser diode at the wavelength of 1.1-1.7 μm wavelengthhas become possible as a result of the present invention as notedbefore. By using the surface-emission laser diode of the 1.1-1.7 μmoscillation wavelength, the inspection of laser elements in the laserdiode array is substantially facilitated. Further, the productivity ofthe optical transmission/reception system is improved remarkably.Construction of such an optical transmission/reception system was notpossible in the conventional surface emission laser diode of 0.85 μmwavelength band. By using the surface-emission laser diode the presentinvention, it became for the first time possible to realize a commercialbase optical transmission/reception system.

[0521]FIG. 61 shows another example of the telecommunication system thatuses a long-wavelength surface-emission laser diode. It should be notedthat FIG. 61 shows an optical fiber 72 drawn out from a module package71 in which a surface-emission laser diode chip is accommodated and anoptical fiber 73 for telecommunication that is connected to the opticalfiber 72. In FIG. 61, those parts explained previously are designated bythe sane reference numerals and explanation is omitted.

[0522]FIG. 61 is referred to.

[0523] The optical fiber 72 drawn out from module package 71 via theconnector 71A is connected by welding or other methods to the opticalfiber 73 for telecommunication at fiber connection part 74. In thiscase, a predetermined connection margin is required. With regard to theoptical fiber cable 72 drawn out from the module package 71, when theoptical fiber length Lg shown in FIG. 61 is too short, a very fine workis needed to assemble the module package 71. Thereby, the productioncost is increased. Also it becomes difficult to produce a high-precisionmodule.

[0524] The optical fiber used in the telecommunication systems of thisinvention is a very minute thing. The diameter is only a 50 μm or 62.5μm in the typical case. When assembling the module package 71 by usingsuch an optical fiber, for example, it is unnecessary to hold theoptical fiber 72 extending from the module package 71 by using a pair oftweezers. Thereby, it is difficult to hold the optical fiber 72 unlessthe length Lg of the optical fiber 72 is less than a certain length.

[0525] Much of the assembling work can be done by an automationapparatus. Even in such a case, a tool is necessary for holding such aminute optical fiber. In consideration of easiness of holding the distalend part of the optical fiber by the holding tool, it is necessary tosecure a certain length Lg for the optical fiber 72.

[0526] The inventor of the present invention, recognizing the importanceof doing the assembly work smoothly, conducted and evaluated extensiveassembly of optical fiber systems. Through various kinds of experimentalproduction operations, it was determined that length Lg shown in FIG. 61must be at least 1 mm. In other words, the length Lg.(the guide opticalfiber length Lg shown in FIG. 61) of the optical fiber 72 drawn out fromthe Module package 71, in which the surface-emission laser diode chip isaccommodated, has to be set to one or more millimeters.

[0527] In the case the length of this part is reduced to the order ofmicrons comparable to the optical fiber diameter, assembling work has tobe done under a microscope, using equipment that is expensive andhigh-precision and highly mechanized. Such work is unrealistic fromindustrial view point.

[0528] It should be noted that such a guide optical fiber 72 isconnected to the optical fiber constituting a part of the opticaltelecommunication system shown in FIG. 61 by welding. Thereby, there isa need to secure a welding margin (margin Gm shown in FIG. 62) in viewof melting of the fiber edge of the guide optical fiber 72. The weldingmargin would be the order of millimeters.

[0529] The inventor of the present invention conducted weldingexperiments and evaluated the necessary length of the welding margin Gmof FIG. 62.

[0530] In the case that guide optical fiber length Lg is in the order ofmicrons, it was discovered that the fiber edge of the optical fiber 71melts excessively. For example, in the case the length Lg is 200 μm, 500μm or 900 μm, the edge surface of optical fiber 71 melted excessivelyand a fine joint was not obtained. On the other hand, it was confirmedthat a fine joint can be obtained in the case the length Lg is made tobe one millimeter or more, such as 1 mm or 3 mm.

[0531] In summary, it is concluded that assembling of then modulepackage 71 requires that the length Lg be one or more millimeters inorder to connect with the optical fiber of the optical telecommunicationsystem to the guide optical fiber.

[0532] With regard to the upper limit of the guide optical fiber 72, itis sufficient for module assembly work to secure the length of 20 mm forthe guiding purpose. In the case the optical fiber 7 is too long, theexcessive optical fiber can be cut after the assembling of the opticalmodule 71 to a suitable length.

[0533] Next is an explanation about another aspect of this embodiment.

[0534] The above explanation discussed the relation with thesurface-emission laser diode 32 acting as the optical source and theguide optical fiber 72, while the same relation holds also at thedetecting side.

[0535] While illustration is omitted, it is, possible to realize aphotodetection unit by replacing the surface emission-laser diode 32 ofFIGS. 61 and 62 with the photodetection device 34 such as photodiode.Thereby, there is an optical fiber corresponding to the guide opticalfiber 72 of FIGS. 61 and 62 in direct contact with the photodetectiondevice 34.

[0536] The same thought is necessary with regard to the moduleassembling and connection to the optical telecommunication system in theside of the photodetection device.

[0537] In the present invention, a highly reliable and practicalassembling of the photodetection unit is achieved by setting the lengthof the guide optical fiber connected directly with the photodetectiondevice 34 (corresponding to the guide optical fiber 72 of FIGS. 61 and62) to one millimeter or more. Further, a reliable connection isachieved with the optical fiber of the optical telecommunication system.

[0538] With regard to the upper limit, a length of 20 mm is sufficientsimilarly to the module package for the optical source side.

[0539] [Tenth Embodiment]

[0540]FIG. 63 shows the example of a telecommunication system that usesthe long-wavelength surface-emission laser diode chip 32 with the laseroscillation wavelength 1.1-1.7 μm band with plural optical fibers. Thoseparts explained previously in the FIG. 63 are designated with the samereference numerals and explanation is omitted.

[0541] In the construction of FIG. 63, the laser diode 32A in the laserdiode chip 32 is driven by a communication control unit 81 via a laserdiode driver circuit 82. The optical signal is supplied to the opticalfibers 72 and 73 in the form of an optical beam.

[0542] Conventionally, an optical telecommunication system was studiedby using the laser oscillation wavelength of 0.85 μm. However, becauseof the large transmission loss in the optical fiber, it was notpractical for long distance telecommunication. Further, in the case ofthe telecommunication system that uses the plural optical fibers incombination of conventional edge-emission type laser diodes, there is aneed of adjusting the optical coupling for each the optical fibers witheach of the laser diodes. Thus, the adjustment process was complicated.Further, it was difficult to connect the laser diodes directly to form atwo dimensional array. Further, in an edge-emission laser diode, theemission angle of the laser beam is large and the laser beam generallyhas a large aspect ratio. Thus, it has been provide a coupling lensbetween the emission part and the optical fiber for better opticalcoupling efficiency.

[0543] Contrary to the prior art, a stable drive is realized with lowenergy and low heating by using the long-wavelength surface-emissionlaser diode of 1.1-1.7 μm band according to this invention.

[0544]FIG. 64 shows the construction of the surface-emission laser diodeof the 1.3 μm band according to this invention. The emission angle ofthe laser beam in such a surface-emission laser diode is smaller ascompared with an edge-emission laser diode and takes the value of about15 degrees in both the vertical and horizontal directions. The laserbeam form is circular, and there is no need of shaping the laser beam.

[0545] Thus, individual laser diodes 32A can be connected withcorresponding optical fibers 72 without using a coupling lens, as longas the irradiation diameter of the laser diode is smaller than the corediameter of the optical fiber 72. The same is true also in otherlong-wavelength bands.

[0546] Thus, by using a surface-emission laser diode according to thepresent invention, the difference between the irradiation diameter ofthe laser diode 32A and the optical fiber core diameter provides atolerable margin, and it becomes possible to adjust plural opticalfibers altogether.

[0547] As shown in FIG. 64, the laser beam that is emitted from anemission part, in other words, the laser diode 32A, is injected withhigh efficiency into the core at the edge surface of the optical fiberThe optical signal thus injected into the optical fiber is transmittedover a long distance with little transmission loss due to the long thewavelength of the optical signal. By using plural optical fibers, a veryhigh quality optical telecommunication system of practical value ismaterialized. The laser diodes 32A can form in arbitrary two-dimensionalarrangement in the surface-emission laser diode chip 32 as long as theydo not cause interference.

[0548] The plural optical fibers 72 are fixed with each other by using ajig 91 shown in FIGS. 65A-65C, in which each of the optical fibers isprovisionally fixed by the jig 91 and pouring a resin 92 into the jig asrepresented in FIG. 65C. Thereby, the positional adjustment can beomitted at the time of system construction, by providing a positioningguide in the connector connection part 71A. Thus, it becomes possible toeasily construct an optical telecommunication system while using pluraloptical fibers.

[0549] Meanwhile, the number of the optical fibers used in an opticaltelecommunication system changes depending on the system. Thus, it isadvantageous to design the system such that the number of optical fiberscan be changed flexibly.

[0550] Thus, as shown in FIG. 66B, a number of openings having the sizeof the optical fiber diameter are formed on the connector connectionpart 71 a, and the connector connection part 71 a is attached on thesurface-emission laser diode chip 32 of FIG. 49C with an adjustment.Further, several kinds of connectors 71 b carrying plural optical fibersas shown in FIG. 66A are provided, and one of the connectors 71 b isselected and inserted into the connector connection part 71 a. By usingsuch a construction, waste of optical fibers in the optical connector71A is eliminated, and it becomes also possible to add optical fiberslater according to the needs. Thereby, it becomes possible to increasethe degree of freedom of design of the optical telecommunication system.

[0551] Furthermore, in long-wavelength surface-emission laser diode chip32 of 1.1-1.7 μm band of this invention, the laser diode elementsconstituting the emission part 32A can be arranged in two-dimensionalarray. In view of this, each optical fiber 95 is provided with a resincoating 96 having a hexagonal cross section as shown in FIG. 67 suchthat the two-dimensionally arranged optical fibers do not contactdirectly with each other Thereby, an optical cable having a closestpacking structure for the optical fibers is realized as represented inFIG. 68. In the optical fiber cable of FIG. 68, the cross-sectional areaof the optical fibers is minimized because of the closest packingarrangement of the optical fibers.

[0552] In the construction of FIG. 67, it is also possible to use afixing member of a resin having a number of holes of hexagonalarrangement for holding the optical fibers, in place of providing aresin coating 96 outside the optical fiber 95.

[0553] [Eleventh Embodiment]

[0554]FIG. 69 shows an example of the optical fiber 101 used in atelecommunication system that uses a long-wavelength surface-emissionlaser diode. Those parts explained previously are designated by the samereference numerals and the description thereof will be omitted.

[0555]FIG. 69 is referred to. The optical fiber 101 is injected with thelaser beam emitted from the laser diode emission part 32A. The opticalfiber 101 consists of cladding 101B enclosing a core 101A, and the core101A transmits the laser beam thus injected. The diameter D of the core101A is determined with regard to the length L so as to satisfy thecondition 105≦L/D≦109.

[0556] Conventionally, an optical telecommunication system was studiedby using the laser oscillation wavelength of the 0.85 μm band. However,the transmission loss of the optical fiber was too large and there wasno practical value. Also there was no laser diode that can oscillatestably in the long-wavelength band, in which the transmission loss isminimum, was not realized. In accordance with the present invention, asurface-emission laser diode oscillating stably at the laser oscillationwavelength of 1.1-1.7 μm band is materialized as a result of improvementof the semiconductor Bragg reflectors 12 and 18 and by the provision ofthe non-optical recombination elimination layers 13 and 17. As a result,a practical long wavelength band optical telecommunication system becamepossible.

[0557]FIG. 70 shows the construction of a long distance opticaltelecommunication system using the above long-wavelengthsurface-emission laser diode chip 32 and the optical fiber 101.

[0558]FIG. 70 is referred to. The long distance opticaltelecommunication system uses the long-wavelength surface-emission laserdiode chip 32. The optical fiber is injected with the laser beam that isemitted from the laser diode emission part 32A of the laser diode chip32. Further, the optical telecommunication system includes a firstoptical fiber 101A having the core diameter D of 50 μm and the length Lof 5 km and second optical fiber having the core diameter D of 50 μm andthe length L of 5 km injected with the laser beam emitted from theoptical fiber 101A, wherein the optical telecommunication system furtherincludes the photodiode chip 34 including the photodetector part 34Ainjected with the laser beam emitted from the second optical fiber 101B.

[0559] Between the laser diode chip 32 and the first optical fiber 101A,the connection module 71 is provided, and a similar connection module 75is provided between the second optical fiber 101B and the photodiodechip 34. Furthermore a repeater 101C is provided between the firstoptical fiber 101A and the second optical fiber 101B for amplificationand the repeating of the optical signal.

[0560] In the constitution of FIG. 70, it should be noted that the firstand second optical fibers 101A and 101B are produced usually withseveral thousand kilometers as a unit. However, a length of severalhundred kilometers becomes the unit of the optical fiber product due toexistence of pores or other defects that occur during the productionprocess. In consideration of transmission loss, the practical length ofthe optical fiber to the repeater 101C is 5-50 km in the case theoptical fiber has a core diameter of 50 μm. The optical fiber of thislength is used for the optical fiber telecommunication.

[0561] In the case the transmission length is longer than 50 km, it isnecessary to provide a relay point for signal amplification in view ofthe transmission loss. When the distance is shorter than 5 m, varioustelecommunication means are available other than the opticaltelecommunication system.

[0562] For optical fiber 101 used with this embodiment, a quartz glassoptical fiber having a core diameter D of several microns, or a plasticsoptical fiber having a core diameter D of several hundreds microns maybe used. These optical fibers can be used alone or in the form of abundle.

[0563]FIG. 71 shows an optical telecommunication system forbi-directional optical telecommunication by using a bundle of quartzglass optical fibers 101-A and 101-B each having a diameter D of 50 μmand a transmission length L of 500 m, wherein these optical fibers areseparated from each other at the photodetection end and the opticalsource end.

[0564]FIG. 71 is referred to.

[0565] There can be seen that optical transmission/reception parts 102Aand 102B are provided in the present invention in which thelong-wavelength surface-emission laser diode chip 32 and the photodiodechip 34 form a pair. Thus, the first optical fiber 101A is coupled tothe emission part 32A of laser diode chip 32 in the opticaltransmission/reception part 102A, and the optical fiber 101A is furthercoupled optically to the optical detection part 34A of photodiode chip34 in the optical transmission/reception part 102B. Similarly the secondoptical fiber 101B is coupled optically to the emission part 32A of thelaser diode chip 32 in the optical transmission/reception part 102B, andthe optical fiber 101B is coupled optically to the optical detectionpart 34A of photodiode chip 34 in the optical transmission/receptionpart 102A. Thereby, the laser diode chip 32 and the photodiode chip 34constituting the optical transmission/reception part 102A form theconnection module 71. Also, the laser diode chip 32 and the photodiodechip 34 constituting the optical transmission/reception part 102B formthe connection module 75.

[0566] By expanding the foregoing construction of using thelong-wavelength surface-emission laser diode chip 32 and thephotodetector chip 34 as a pair for the case in which a number of laserdiode elements 32A are formed on the laser diode chip 32 and a number ofphotodiode elements are formed on the photodetector chip 34, it ispossible to realize a large capacity optical telecommunication system.

[0567]FIG. 72 shows the case of applying the present invention to a highspeed multimedia network that uses a fluorinated plastic optical fiberhaving a core diameter of 100 μm and the transmission length of lessthan 100 m.

[0568]FIG. 72 is referred to.

[0569] A first optical fiber 111 having a core diameter D of 50 μmextends from a station-side apparatus 110 and a second optical fiber112, formed by bundling 50 optical fibers each having a core diameter Dof 50 μm and a length of 1 km, is connected to the optical fiber 111. Asa result, there is formed a the high speed optical transmission systemcapable of transmitting information with the speed of the order of Gbpswith a total distance of 100 km. In the example of FIG. 72, the opticalrepeater 111R is provided between the optical fiber 111 and opticalfiber 112, to compensate for the damping of the signal by thepropagation loss of quartz glass optical fiber.

[0570] The optical signal transmitted through the second the opticalfiber 112 enters into a network terminator 115 at first and converted toan electric signal. Further, the electric signal is distributed tonecessary lines 115 a−115 c, and the electric signal thus supplied toeach line is transmitted further in the form of the optical signal by anoptical telecommunication system 116 that includes the opticaltransmission/reception parts 102A and 102B explained to with referenceto FIG. 71. The optical signal thus transmitted is supplied to acorresponding optical output port. In the optical telecommunicationsystem 116, an optical fiber 117 a having a core diameter of 100 μm anda length of 10 m is used for the optical transmission to the opticaloutput port corresponding to the line 115 a, while an optical fiber 117b having a core diameter of 100 μm and a length of 50 m is used for theoptical transmission to the optical output port-corresponding to theline 115 b. Further, an optical fiber 117 c having a core diameter of100 μm and a length of 100 m is used for optical transmission to theoptical output port corresponding to the line 115 c. The optical signalsthus transmitted are converted to electric signals by the opticaltransmission/reception part 102B in each optical output port and issupplied to corresponding terminal devices 102C.

[0571] Further, the transmission from each terminal device 102C istransmitted to the optical transmission/reception part 102 A in the formof an optical signal through the optical fibers 117 a-117 c and reachesthe station-side apparatus 110.

[0572] In this embodiment, the core diameter of the optical fibers 117a-117 c has a large value of 100 μm, and high-precision alignment byusing a high-precision lens system is not necessary. Thus, it becomespossible to achieve optical connection to various apparatuses in a homeor office quite extremely.

[0573] In the present embodiment, too, the relationship of 105≦L/D≦109is maintained between the length L and core diameter D of the opticalfibers. When the transmission distance is longer than 100 km, nosubstantial transmission is possible due to the transmission loss, andthus, it is necessary to provide a relay point for amplification andrepeating. In the case the transmission distance is shorter than 10 m,such an optical telecommunication system is not always necessary and maybe replaced with other means.

[0574]FIGS. 73A and 73B show the application of the long-wavelengthsurface-emission laser diode of the present invention to a hybridoptical integrated circuit device, respectively in a plane view and across-sectional view.

[0575]FIGS. 73A and 73B are referred to. The long-wavelengthsurface-emission laser diode chip 32 and the photodiode chip 34 arecarried on a ceramic substrate 51 in this embodiment. Further, theceramic substrate 51 carries thereon a first optical waveguide 52 havinga rectangular cross-section of 7×7 μm and a length of 1 cm for guidingthe laser beam emitted from the laser diode 32A. Further, the ceramicsubstrate 51 carries a second optical waveguide 53 having a rectangularcross-section of 7×7 μm and a length of 1 cm similar to the opticalwaveguide 52 in optical coupling with the photodetector part 34 A of thephotodiode chip 34 for supplying the optical signal to the photodetectorpart 34B. Further, a preamplifier 51 for amplifying the output electricsignal of the photodetector chip 34 is provided on the ceramic substrate51.

[0576] Further, an optical fiber 54 having a core diameter D of 100 μmand a length of 100 m is provided in optical coupling with the firstoptical waveguide 52 via a connection module 56, and a second opticalfiber 55 having a core diameter D of 100 m and a length of 100 m isprovided in optical coupling with the second optical waveguide 53.

[0577] Further, a connection module 57 equipped with thesurface-emission laser diode chip 32 and the photodiode chip 34 isprovided at the other end of the optical fibers 54 and 55 such that theoptical fiber 54 is coupled with the photodetector part 34A of thephotodiode chip 34 and the optical fiber 55 is coupled with the laserdiode 32A of the laser diode chip 32.

[0578] The optical waveguides 53 and 54 are formed on a siliconsubstrate 58 by the steps of forming the respective cores and thecladdings that cover the cores by a photolithographic process, and thesilicon substrate 58 is provided on the ceramic substrate 51 commonlywith the preamplifier 51A.

[0579] [Twelfth Embodiment]

[0580]FIGS. 74A and 74B show an example of a laser diode chip 120 thatis used with the optical telecommunication system in which thelong-wavelength surface-emission laser diode of the present invention isused, wherein FIG. 74A shows a plane view while FIG. 74B shows across-sectional view taken along a line A-A′. It should be noted thatthe scale FIG. 74A is not identical with the scale of FIG. 74B. In thedrawings, those parts explained previously are designated by the samereference numerals and the description thereof will be omitted.

[0581]FIGS. 74A and 74B are referred to.

[0582] It can be seen that the long-wavelength surface-emission laserdiode 32A and the photodetection device 34A are formed to monolithicallyon a laser diode chip 120.

[0583] The photodetection device 34A has a stacked structure similar tothe stacked structure of the long-wavelength surface-emission laserdiode 32A and is formed simultaneously with the process of forming thesurface-emission laser diode 32A. The structure thus formed can be usedas a photodetection device, by applying with a reverse bias or usingwithout a bias. This photodetection device 34A has sensitivity to theoscillation wavelength of the surface-emission laser diode 32A and candetect the optical emission of the laser diode 32A.

[0584] As will be understood from the plane view of FIG. 74A, thephotodetection device 34A is formed in such a form to surround thelong-wavelength surface-emission laser diode 32A. On the top surface ofthe laser diode 32A, an upper electrode 121 is formed and a lowerelectrode 123 is formed on the bottom surface of the laser diode chip120. Also another upper part electrode 122 is formed on the top surfaceof the photodetection device 34A. An optical window is formed in theupper part electrode 121 of the laser diode 32A for taking out theoptical output. Such a window is not formed in upper part electrode 122the of photodetection device 34A.

[0585]FIG. 75 is the figure that explains the operation of the laserdiode chip 120 shown in FIG. 74.

[0586]FIG. 75 is referred to.

[0587] The laser diode 32A in the surface-emission laser diode chip 120is positioned so as to face the end surface of an he optical fiber 125,and the optical beam emitted from the surface-emission laser diode 32Ais injected into the core of the optical fiber. Thereby, there occurs aleakage light in the lateral direction from the sidewall of thesurface-emission laser diode 32A, and the leakage light is detected bythe photodetection device 34A provided adjacent to the laser diode.While the amount of the leakage light from the sidewall of thesurface-emission laser diode 32A is not much, nevertheless the leakagelight is detected by the photodetection device 34A, as thephotodetection device 34A is formed so as to surround thesurface-emission laser diode 32A in the construction of FIG. 75.

[0588] Furthermore, it should be noted that the semiconductor Braggreflector 18 and the upper part electrode 122 are formed on thephotodetection device 34A in FIG. 75. Therefore, the optical signal andthe like transmitted from another party via the optical fiber 125 isreflected at the surface of the photodetection device 34A as shown withthe arrow in the drawing. Thereby, the photodetector 34A does not detectsuch an optical signal.

[0589] As it will be clear from the aforementioned explanation, thepresent invention forms the photodetection device for detecting theoutput detection of the surface-emission laser diode integrally on thesurface-emission laser diode chip. By integrating such a laser diodechip on a ceramic substrate 111, it becomes possible to construct theoptical telecommunication system having a hybrid constitution.

[0590]FIGS. 76A and 76B show an example of the semiconductor laser diodechip used with the optical telecommunication system in which thelong-wavelength surface-emission laser diode of this invention is used,wherein FIG. 76A shows a plane view while FIG. 76B shows across-sectional view that taken along a line A-A′. The scale of FIG. 76Aand FIG. 76B are not the same.

[0591]FIGS. 76A and 76B are referred to.

[0592] The long-wavelength surface-emission laser diode 32A and thephotodetection device 34A are integrated monolithically on a laser diodechip, wherein the photodetection device 34A has a stacked structuresimilar to the stacked structure of the long-wavelengtlisurface-emission laser diode 32A.

[0593] Thus, the photodetection device 34A is formed simultaneously withthe same process as the one used for forming the surface-emission laserdiode 32A The photodetection device 34A thus formed has sensitivity tothe wavelength of the surface-emission laser diode 32A and can detectthe optical radiation produced by the laser diode 32A.

[0594] In the present embodiment, the upper semiconductor Braggreflector 18 is removed from the photodetection device 34A by an etchingprocess. As can be seen from the plane view of FIG. 76A, thephotodetection device 34A is formed so as to surround thelong-wavelength surface-emission laser diode 32A, and the devices 32Aand 34A have respective top surfaces provided with the upper electrode121 and the upper electrode 122 formed with the window for opticalinput/output. Further, the bottom electrode 123 is formed on the bottomsurface of laser diode chip 120.

[0595]FIG. 77 explains the operation of the laser diode chip of FIG. 76.

[0596]FIG. 77 is referred to.

[0597] In the surface-emission laser diode chip 120, the laser diode 32Ais positioned so as to face the end surface of the optical fiber 125such that the optical beam emitted from the surface-emission laser diode32A enters into the core of optical fiber 125.

[0598] In this embodiment, the sidewall of the surface-emission laserdiode 32A and the sidewall of the photodetection device 34A are coveredwith the upper part electrode 121 or 122, and the leakage s light is notformed at the side wall of the laser diode.

[0599] Thereupon, when an optical beam carryhinig an optical signalcomes in from another party on the line, the optical beam emitted fromthe end surface of the optical fiber 125 enters into the top surface ofthe photodetection device 34A while causing spreading as represented byan arrow in the drawing. The optical beam is then detected by thephotodetection device 34A formed so as to surround the surface-emissionlaser diode 32A. On the other hand, the top surface of surface-emissionlaser diode 32A is covered with the semiconductor Bragg reflector 18,and because of this, no substantial optical beam invades inside thesurface-emission laser diode 32A from outside.

[0600] Thus, as will be clear from the aforementioned explanation, itbecomes possible to construct an optical telecommunication system havingan optical transmission/reception unit of hybrid construction in thepresent embodiment, by forming the photodetection device 34A formonitoring the output of the surface-emission laser diode 32A integrallyon the surface-emission laser diode chip 120. Such a laser diode chip120 can be integrated on the ceramic substrate 111.

[0601] Furthermore the combination of the surface-emission laser diodeand the photodetection device that explained above is merely for thepurpose showing an example, and the present invention also includes thecase of forming an array of these devices or the case of combining themonitoring photodetector 34A for monitoring the output of thesurface-emission laser diode 32A and the photodetector 34A for detectingthe incoming signals are combined. Naturally, the present invention isnot limited to the specific mutual positional relationship or shape ofthe surface-emission laser diode and the photodetector.

[0602] [Thirteenth Embodiment]

[0603] Next, this invention will be explained about other examples.

[0604] It is important to use a highly strained layer of GaInAs, GaInNAsor GaAsSb for the active layer in order to realize the long wavelengthsurface emission laser diode of 1.1-1.7 μm. In order to achieve this, itis necessary to minimize the mechanical stress applied to the laserdiode. Such a mechanical stress may result from the thermal stresscaused between the laser diode and the mount substrate as a result ofthe operational temperature environment or due to the heating of thelaser diode or driver circuits. Such a thermal stress is caused in astructure in which materials of different linear thermal expansioncoefficients are fixed, due to the tendency of the structure that tendsto maintain original shape. Thus, the thermal stress depends on thetemperature change, the coefficient of linear thermal expansion, Youngmodulus, and the like. It is possible to eliminate the thermal stress bycontrolling the temperature of the whole module including the laserdiode. However, such a measure of providing a temperature regulatingmechanism is difficult in view of the increased cost. Further, it isdifficult to control the temperature completely constant.

[0605] Thus, it is desirable, in order to provide a highly reliablesystem with low cost, to use a material having a coefficient of linearthermal expansion close to that of the laser diode for the mountsubstrate so as to reduce the influence of the thermal stress on thelaser diode as small as possible.

[0606] In this embodiment, various mount substrates were produced byusing various materials having different coefficients of linear thermalexpansion and evaluation was made about the influence of the thermalstress on the output characteristic of the laser at the time of thelaser oscillation. The surface-emission laser diode used in theexperiment has the structure explained with reference to FIG. 1 and thelaser oscillation wavelength was 1.3 μm. Further, a chip size of 5 mm×10mm (thickness 0.6 mm) was used in which 20 laser diodes were alignedwith a pitch of 300 μm. The size of the mount substrate made was 10mm×20 mm (thickness 2 mm).

[0607] The result is shown in Table 5. In Table 5, ∘ represents thesample in which a stable output was obtained in the operationalenvironment of 0-70° C. while × represents the sample in which no stableoutput was obtained and hence not suitable for practical use. TABLE 5linear thermal expansion material coefficient laser output quartz glass0.3 × 10⁻⁶/κ   X smicrystal 2 × 10⁻⁶/κ X CVD diamond 2 × 10⁻⁶/κ X Si 4 ×10⁻⁶/κ ◯ SiC 4 × 10⁻⁶/κ ◯ AlN 5 × 10⁻⁶/κ ◯ GaAs 6 × 10⁻⁶/κ ◯Al-Si_((60Al-40Si)) 15 × 10⁻⁶/κ  X Cu 17 × 10⁻⁶/κ  X

[0608] The coefficient of linear thermal expansion of the laser diode ofthis invention is 6×10⁻⁶/K. From the above results, it can be seen thatthe thermal stress is reduced and a stable laser output is obtained whenthe difference of the linear thermal expansion coefficient between thelaser diode and the mount substrate within about 2×10⁻⁶/K. Particularly,the materials such as Si, SiC, GaAs, AlN are easily available and areeasily processed and handled for the mount substrate.

[0609] Further, by choosing the heat radiating member on which the mountsubstrate is mounted such that the material of the heat radiating memberhas a linear thermal expansion coefficient close to that of the laserdiode, the stress to the mount substrate is minimized and the mechanicalstress applied to the laser diode is reduced as a result. Further, thematerial constituting the heat radiation member is required to have ahigh thermal conductivity.

[0610] In the present invention, various heat radiating members areformed by using various materials having different linear thermalexpansion coefficients and the effect of heat generated at the time ofthe laser oscillation on the laser output characteristics is evaluated.

[0611] The laser diode used for the evaluation was the same as the oneused in the evaluation of Table 5. In this experiment, an SiC substratehaving the same size as in the previous experiments was used for themount substrate.

[0612] Table 6 shows the results, wherein ∘ in Table 4 represents thesample in which a stable output was obtained in the operationalenvironment of 0-70° C., while × represents the case in which no stableoutput was obtained. TABLE 6 material thermal conductivity laser outputSiO2  about 8 W/mK X Al2O3  about 17 W/mK X Cobar  about 17 W/mK X AlNabout 200 W/mK ◯ Cu/W  180-200 W/mK ◯ W about 170 W/mK ◯ Mo about 160W/mK ◯ Cu about 390 W/mK ◯

[0613] The thermal conductivity of the laser diode of this invention is55W/mK. Thus, from the results noted above. it can be seen that apreferable result is obtained when the thermal conductivity of the heatradiating member is larger than the thermal conductivity of the laserdiode. Thus, the heat generated at the time of the laser oscillation istransferred to the mount substrate and then to the heat radiation memberwithout returning to the laser diode when the thermal conductivity ofheat radiating member is larger than the thermal conductivity of thelaser diode of this invention. Thus, the output fluctuation of the laseraccompanied by the effect of heat accumulation does not result and astable characteristic suitable for practical use is obtained.Particularly, the materials such as AlN, Cu/W, W, Mo, Cu are easilyavailable and can be processed easily to form a heat radiating member.

[0614] Especially the use of Cu/w is advantageous as it allows controlof the thermal conductivity by controlling the compositional ratio andcan be used as a he package substrate to be explained later withreference to FIG. 79.

[0615] Hereinafter, an optical telecommunication system of the presentembodiment that uses such a member will be explained.

[0616] The telecommunication system is composed of the optical fiber oroptical waveguide that operates as the transmission path between thephotodetection part including a surface photodetection device and adriver circuit thereof and the optical transmission part including asurface-emission laser diode and a driver circuit.

[0617] The driver circuit of the laser diode or the photodetector isformed on the same mount substrate commonly with the laser diode of thephotodetector to which the drive circuit cooperates, Alternatively, thedriver circuit is formed on the laser diode substrate by a wafer processsimultaneously to the process of forming the respective devices to whichthe driver circuit cooperates. Further, the optical telecommunicationsystem performs the bi-direction telecommunication by providing theoptical transmission part and the photodetection part at both ends ofthe optical transmission path.

[0618]FIG. 78 shows an example of the optical transmission part of suchan optical telecommunication system. In the drawing, those partsexplained previously are designated by the same reference numerals andthe description thereof will be omitted.

[0619]FIG. 78 is referred to.

[0620] The optical transmission part includes the surface-emission laserdiode chip 32 and a driver circuit 320R driving the laser diode chip 32,a mount substrate 131 on which the laser diode chip 32 and the drivercircuit 32DR are mounted, a heat radiation member 132 adjustablysupporting the mount substrate 131 and for radiation of the heat, and ametal package 133 holding the heat radiation member 132 and acting asthe heat sink or heat radiation fin, and an optical transmission 134acting as the optical path. The metal package 133 and heat radiationmember 132 and also mount substrate 131 are connected mechanically andthermally with each other by a solder or a resin. Also, the laser diode32 and the driver circuit 32DR are connected electrically by wirebonding, and the like.

[0621] For example, the laser diode chip 32 includes the laser diode ofFIG. 1, wherein the laser diode may be the one that oscillates at thewavelength of 1.2 μm. As for the mount substrate 131, on the other hand,a Si substrate having the the coefficient of linear thermal expansion of4×10⁻⁶/K can be used. In this case, the laser diode 32 is die-bondedwith an AuSn solder on the mount substrate 131. Thereby, electrode andelectric mechanical connection are achieved.

[0622] It should be noted that an SiO₂ film 200 nm thickness is formedon the surface of the Si substrate 131. This SiO₂ film may be formed bya thermal oxidation process or a CVD process or an SOG process. Theforegoing oxide film is used for insulation, but the heat radiationcharacteristic of such a film is inferior to Si. Therefore, it ispreferable that the insulation film has as small thickness as possiblewithin the range of providing sufficient electric insulation. The oxidefilm may be omitted if it is possible. The driver circuit 32DR thatdrives the laser diode chip 32 is mounted on the same mount substrate131 together with the laser diode chip 32. A thermal conductive AlNsubstrate (coefficient of linear thermal expansion 5×10⁻⁶/K, thermalconductivity 200W/mK) may be used as the heat radiating substrate thatcarries the mount substrate. The AIN substrate has excellentcompatibility with regard to the coefficient of linear thermalexpansion. Further, a powder mold product of Cu/W may be used for themetal package 133. For example, the molded of Cu/W product forming themetal package 133 may have the composition of 89W-11Cu and a linearthermal expansion coefficient of 6.5×10⁻⁶/K and a thermal conductivityof 180W/mK. By using such a powder mold product, a highly precisionproduct is obtained with low cost. Further, it is possible to form heatradiation fins easily and efficient heat radiation becomes possible.

[0623] In the example of FIG. 78, a multiple mode optical fiber having acore diameter of 50 μm is connected optically as the optical fiber 134with the laser diode 32A in the laser diode chip 32. The stability ofsuch an optical telecommunication system was evaluated in theoperational environment of 0-70° C. from and it was confirmed that thelaser output is stable No change of output characteristics was observed.Further, there was no lifetime degradation. Thus, it was found that anexcellent optical telecommunication system can be constructed.

[0624] Furthermore, It is possible to use a GaAs (coefficient of linearthermal expansion 6×10⁻⁶/K) or AlN (coefficient of linear thermalexpansion 5×10⁻⁶/K) or SiC (coefficient of linear thermal expansion4×10⁻⁶/K) for the substrate as the mount substrate 133 instead of the Sisubstrate. Because these substrates are an insulating substrate,formation of oxide film is not necessary when these substrates are usedOtherwise, the same structure may be used. In view of the cost andeasiness of handling, the use of AlN is most preferable.

[0625] Also, good results were obtained when Cu/W (coefficient of linearthermal expansion is 6−8×10⁻⁶/K, thermal conductivity is 180-200W/mK)such as 89W-11Cu, 85W-15Cu or 80W-20Cu, or the metals of W, Mo, Cu areused for the heat radiation member in place of AIN.

[0626] In the example of FIG. 78, it was explained based on theconstruction that there is only one laser diode in the laser diode chip32 forming the transmission part. However, it is possible to form anarray of plural laser diodes also in the laser diode chip 32 or, byforming the array of the laser diode chip 32. Thereby, a large capacityoptical telecommunication system is constructed.

[0627] For example, in the case of the multiple laser array chip inwhich plural laser diodes 32A are formed on a single chip 32, the laserdiodes 32A come close with each other and the fluctuation of the laseroutput characteristic may be influenced by the thermal stress caused bythe heat generation and accumulation of the heat thus generated.Furthermore the laser diode driver circuit 32DR is often formed also onsuch a chip. Thus, the heat from such a driver circuit 32DR issuperimposed. In this, embodiment, the laser output that stabilizedwithout bringing about such a problem by choosing the material of themount substrate 131 or the heat generation part 132 appropriately.

[0628] Formerly, the surface-emission laser diode having the oscillationwavelength of 1.1-1.7 microns did not exist. Therefore, thetechnological problems with regard to the optical telecommunicationsystem or mounting of the surface-emission laser diode chip of such along-wavelength band have not been announced. This time, the inventor ofthis invention recognized the concrete technological problems for thefirst time by this invention and provided the resolution.

[0629] In the explanation above, a multimode optical fiber was used forthe optical transmission path coupled optically to the laser diode chip32. However, the optical transmission path may also be a single modeoptical fiber or a plastic optical fiber. The laser diode of the presentinvention does not need expensive cooling device such as a Peltierdevice. But the present invention does not exclude the use do such acooling device.

[0630] Next, another embodiment of the present invention will beexplained with reference to FIG. 79, wherein those parts correspondingto the parts described previously are designated by the same referencenumerals and the description thereof will be omitted.

[0631] Referring to FIG. 62, the present embodiment also shows theoptical transmission part of the optical telecommunication system. Inthe present embodiment, the heat radiating member 132 functions also asthe metal package 133.

[0632] It should be noted that the illustrated optical transmission partincludes the laser diode chip 32 in which a number of laser diodes 32Aare arranged in the form of laser array, the driver circuit 32DR drivingthe laser diodes 32A, a mount substrate on which the laser diode chip 32and the driver circuit 32DR are mounted, a metal package 133 supportingthe mount substrate 131 and functioning as the heat sink and also a heatradiating fin, an optical fiber 134 constituting the opticaltransmission path, and a ferule fixing the optical fiber 134. A solderor a resin connects the metal package 133 and the mount substrate 131mechanically and thermally. Further, the laser diode chip 32 and thedriver circuit (not shown) are connected electrically by using a bondingwire.

[0633] In the illustrated example, the laser diode of FIG. 27 having theoscillation wavelength of 1.3 μm is used, and four devices are arrangedwith a pitch of 250 μm, which is the pitch identical with the pitch ofthe corresponding optical fibers. Similarly to the previous embodiments,a Si substrate was used for the mount substrate and the laser diode wasdie bonded on the mount substrate by using an AuSn solder. Further, theelectrodes are connected mechanically and electrically.

[0634] It should be noted that the surface of the Si substrate is formedwith an SiO2 film having a thickness of 200 nm by a thermal oxidationprocess. However, such an oxide film may be formed by a CVD process oran SOG process. Further, in view of the heat radiating performance ofthe SiO₂ film, it is preferable to form the SiO2 film with a thicknessas small as possible. The SiO2 film may be omitted if it is possible.Similarly, the driver circuit (not shon) that drives the laser diode isformed also on the common mount substrate.

[0635] As the metal package supporting the mount substrate and actingalso as the heat radiating member, a powder mold product of Cu/W is usedFor example, the molded of Cu/W product forming the metal package mayhave the composition of 89W-11Cu and a linear thermal expansioncoefficient of 6.5×10⁻⁶/K, which is close to the linear thermalexpansion coefficient of the laser diode. Further, the metal package hasa thermal conductivity of 180W/mK. By using such a powder mold product,a highly precision product is obtained with low cost. Furthers it ispossible to form heat radiation fins easily and efficient heat radiationbecomes possible.

[0636] In the present embodiment, an array of multimode optical fibersin which the optical fibers each having a core diameter of 50 μm arearranged with a pitch of 250 μm is used. In the temperature range of0-70° C., there occurs no change of laser output and no lifetimedegradation. Thus, excellent optical telecommunication becomes possible.As the metal package functions also as the heat radiating member, thenumber of parts can be reduced and the efficiency of heat radiation ismaximized.

[0637] A similar result is obtained also when a GaAs substrate or AlNsubstrate is used in place of the Si substrate. In the case of the AlNsubstrate or SiC substrate, they are insulating substrates and theformation of the oxide film is not necessary. Otherwise, the foregoingdescription applies and further explanation will be omitted.

[0638] In the present embodiment, four laser diodes and four opticalfibers are used However, the present invention is by no means limited tothis specific construction but the present invention is applicable alsoto the case in which the number of the laser diode is one and the numberof the optical fiber is one, or the number of the laser diodes is 8, 12,11 and there are 8, 12, 16 optical fibers in correspondence thereto.

[0639] In the case of the multi-laser diode array chip in which aplurality of laser diodes are formed on a common chip by exploiting thefeature of the surface-emission laser diode of the present invention, alarge number of laser diodes can be formed easily and is ideal for largecapacity telecommunication. On the other hand, in the case of such amulti-laser array chip, heat dissipation of the laser diodes becomes animportant issue. By using the material of the mount substrate and theheat radiating member as set forth in the present embodiment, it becomespossible to operate the laser diode array without causing problems.Thereby, a stable laser output can be obtained.

[0640] In the present embodiment, a multimode optical fiber was usedalso for the optical transmission path. However, this is not a mandatorycondition and it is possible to use an optical waveguide, single modeoptical fiber, plastic optical fiber, and the like.

[0641] [Fourteenth Embodiment]

[0642] Next a telecommunication system according to another embodimentof the present invention that uses the long-wavelength surface-emissionlaser diode of the present invention will be explained with reference toFIG. 80. In FIG. 80, those parts corresponding to the parts describedpreviously are designated by the same reference numerals and thedescription thereof will be omitted.

[0643] Referring to FIG. 80, the telecommunication system that uses thelong-wavelength surface-emission layer diode includes a laser diodemodule 141 carrying thereon the laser diode chip 32, a ferule 142Afixing the optical fiber 142, an adapter housing 143 accommodating theferule 142A together with the optical fiber 142, a bush 144 fixing theoptical fiber 142, a housing 145 accommodating the bush 144, and thebase 146 that holds the laser module 141 and the housing 143 as anintegral body; In the construction of FIG. 63, the length of the opticalfiber 142 from the point A to the point B is set longer than thedistance L (fixed distance) between the end surface of the adapterhousing 143 at the side of the laser diode chip 32 and the end surfaceof the housing 145.

[0644] More particularly, in the case the fixed length L is set to 1 inFIG. 80, the length A-B of the optical fiber 142 is set to 1.05.Thereby, the optical fiber 142 is provided with a bend, and theresilience associated with the bend causes the optical fiber 142 to beurged in the axial direction toward the optical emission part 32A (leftdirection in the drawing). Thereby, the mechanical connection isstabilized and an excellent optical coupling can be realized. Here, aplastic optical fiber is used as the optical fiber 142 but the presentinvention is by no means limited to such a specific case and it ispossible to use a quartz glass fiber having a plastic coating.

[0645]FIG. 81 shows the case in which the length L of FIG. 80 is set to1 and the length A-B of the optical fiber is set to 2. Other conditionsare identical with the case of FIG. 80. In the present embodiment, alarger resilient force is obtained as compared with the case of FIG. 80and the connection between the laser diode and the optical fiber becomesmore reliable.

[0646]FIG. 82 shows the cross-sectional view of the adapter housing 143used in the optical telecommunication system of FIG. 80 or 81.

[0647] Referring to FIG. 82, the adapter housing 143 includes a taperedsplit sleeve 1431, a ferule 142A fixing the optical fiber 142, a coilspring 1432 of a shape-memory alloy exerting a force in the axialdirection, a collar 1433 cooperating with the coil spring 1432 and aplug housing 1434 accommodating therein the split sleeve 1431, the coilspring 1432 and the collar 1433, and a connecting member 1435 forconnecting the plug housing 1434 to the adapter housing 143.

[0648] The coil spring 1432 exerts a resilient force at the ordinarytemperature or heated state determined by the initial shape. Thus, withcooling, the coil spring may extend and urge the ferule 142A in theaxial direction thereof. Depending on the design of the connectingmember 1435, it is possible to memorize the shape such the coil spring1432 extends at the high temperature side.

[0649]FIG. 83 shows a modification of FIG. 82, wherein those partscorresponding to the parts described previously are designated by thesame reference numerals and the description thereof will be omitted.

[0650] Referring to FIG. 83, the coil spring 1432 of the shape-memoryalloy is replaced with a leaf spring 1432A of a shape-memory alloy andthe leaf spring exerts a resilient force at the ordinary temperature orat the heated state determined by the initial shape of the spring. Thus,the leaf spring 1432A may extend with cooling and urge the optical fiber142 in the axial direction thereof. Depending on the design of theconnecting member 1435, the leaf spring 1432A may extend at the hightemperature side.

[0651] It should be noted that the spring 1432 or 1432A is not limitedto a shape-memory alloy but may be formed of a shape-memory plastic. Insuch a connection module, there exists a temperature difference betweenthe temperature in which the optical telecommunication system isassembled (generally higher than the room temperature) and thetemperature (room temperature) in which the system is used. Because ofthis temperature difference, the shape-memory material changes the shapethereof and generates a resilient force in the state that the member isassembled in a structural body. It should be noted that the sense oftemperature change (between the state in which the system is assembledand the state in which the system is used) may be reversed.

[0652]FIG. 84 shows another example of the telecommunication system thatuses the long-wavelength laser diode according to the present invention,wherein those parts corresponding to the parts described previously aredesignated by the same reference numerals and the description thereofwill be omitted.

[0653] Referring to FIG. 84, the telecommunication system of the presentembodiment is formed of a laser module 141 carrying the laser diode chip32, a ferule 142A for fixing the optical fiber 142, an adapter housing143 accommodating the ferule 142A therein together with the opticalfiber 142, a fixing apparatus 147 holding and fixing a part of theoptical fiber 142, and abase 146 fixing the adapter housing 143 and thefixing apparatus 147 and the laser module 141 as an integral body.Thereby, the telecommunication system of FIG. 67 provides a bend to theoptical fiber 142 between the adapter housing 143 and the optical fiberfixing apparatus 147.

[0654] The optical fiber fixing apparatus 147 is a device that uses africtional grip compression and includes a shape-memory alloycompressional spring 1471, a collar 1472 cooperating with the spring1471, another collar 1473, a ball 1474 disposed between the collars 1472and 1473, and a housing 1475 having a conical surface in contact withthe ball 1474. In the housing 1475, the ferule 142B holding the opticalfiber 142 and the split sleeve 1476 are accommodated in the state thatthe shape-memory alloy spring 1471 intervenes between the collar 1472and the split sleeve 1476.

[0655] In the optical telecommunication system of such a construction,the fiber 142 urges a force acting in the left and right directions uponthermal deformation, while such an urging force pushes the ball 1474 inthe optical fiber fixing apparatus 147 in the right direction by theaction of the compressional spring 1471. Thus, the optical fiber 142cannot move in the right direction and exerts a force to the side of theadapter housing at the opposite side.

[0656] In the example of FIG. 63, the optical fiber 142 is provided witha bend and the optical fiber 142 urges the optical fiber 142 in thedirection of the laser diode chip 32 as a result of the resilient forceassociated with the bend of the optical fiber 142. In the example ofFIG. 84, the resilient force of the optical fiber 142 is boosted withthe superimposed resilient force of the spring 147 of the shape memoryalloy, and the optical fiber 142 is urged more effectively to thedirection of the laser diode chip 32.

[0657]FIG. 85 shows the optical connector formed of the tapered splitsleeve 1431, the ferule 142A holding the optical fiber 142, the coilspring 1432 applying an axial urging force to the ferule 142A, thecollar 1433, a plug housing 1434 accommodating therein the split sleeve1431, the coil spring 1432 and the collar 1433, and the adapter housingaccommodating the ferule 142B and the plug housing 147, wherein theoptical connector having such a construction is connected with anotheroptical connector by connecting the respective connector housings 143with each other by way of a connecting screw 1436.

[0658] In the construction of FIG. 65, it should be noted that the coilspring 1432 exerts an urging force at the normal temperature as a resultof the initial shape thereof. Thus, the coil spring 1432 is extended atthe normal temperature change, and the ferule 142A is urged in thedirection of the axis of the optical fiber 142. Thereby, two opticalfibers are connected effectively. In this example, too, it is possibleto use various shape memory alloys and shape memory plastics. In theexample noted above, the present invention was explained with referenceto the example that uses a shape-memory alloy for the spring. However,it is possible to use an ordinary resilient material such as copperbronze or urethane foam. By using such well-known art, it is possible toreduce the cost of the module.

[0659] [Fifteenth Embodiment]

[0660] Next, a further embodiment of the present invention will beexplained.

[0661]FIG. 86 shows an example of the construction of the opticaltransmission part that is provided with the optical telecommunicationsystem that uses the surface-emission laser diode of the presentinvention. In FIG. 86, those parts explained previously are designatedby the same reference numerals and the description thereof will beomitted.

[0662]FIG. 86 is referred to.

[0663] In the present embodiment, a connector substrate 151 holdingplural optical fibers 142 on the mount substrate 131 is provided suchthat each of the plural surface-emission laser diodes 32 forming a partof the array opposes with a corresponding one the plural optical fibers142. Further, plural photodetection devices 142P are provided on theconnector substrate 151 so as to monitor the optical power of thesurface-emission laser diodes 32, such that the photodetection devices142P correspond respectively to the plural optical fibers 142. Each ofthe photodetection device 142P is provided as it face the correspondingsurface-emission laser diode 32 for detecting the optical beam emittedtherefrom.

[0664] In FIG. 86, it can be seen that the laser diode chips 32, theoptical fibers 142 and the monitoring photodetectors 142P are arrangedto form a one-dimensional array. However, a similar effect is achievedalso when the photodetectors 142P are disposed in a two-dimensionalarray. In this drawing, each of the laser diodes is represented as anindependent chip 32. However, the laser diodes may be the one formed ona common chip 32.

[0665] In FIG. 86, illustration of the driver circuit of thesurface-emission laser diode 32 or the laser output control circuit forfeedback control of the laser output based on the signals acquired fromthe driver circuit or monitoring photodetection device is omitted forthe sake of simplicity.

[0666] In the example of FIG. 86, the connector substrate 151 holds theoptical fiber 142 and is mounted on the mount substrate 131 by using aconnector guide 151A.

[0667] Each of the optical fibers is held in a penetrating hole providedin the connector substrate surface 151 so that the end surface of theoptical fiber faces a corresponding laser diode element 32A in the laserdiode chip 32. Further, each laser diode elements 32A and thecorresponding optical fiber 142 are aligned optically. Further, there isprovided a monitoring photodetector 142P in the vicinity of the opticalfiber insertion hole of the connector substrate 151.

[0668] Here, the majority of the laser beam emitted from thesurface-emission laser diode is infected into the optical fiber 142aligned to the laser diode. On the other hand, the part of the laserbeam failed to enter the optical fiber 142 is detected by thephotodetection device 142P.

[0669]FIG. 87 shows the block diagram of the control system thatstabilizes the output of the surface-emission laser diode 32 by usingthe monitoring photodetector 142P shown in FIG. 86.

[0670] Referring to FIG. 87, the surface-emission laser diode 32 isdriven by a laser drive circuit 161 to which the data signal (electricalsignal) is supplied, and there is formed a laser bean as a result. Apart of the laser beam thus formed is detected as the leakage light, andthe output electrical signal of the photodetector 142P is supplied to afeedback control circuit 162. The feedback control circuit 162 in turncontrols the laser driver circuit 161 so as to compensate for the changeof the output electrical signal of the photodetection device 142.

[0671] It should be noted that no strong optical power is needed for thelaser beam detected by the monitoring photodetector 142P, as themonitoring photodetector merely detects the change of the laser outputfor feedback control. From the viewpoint of long range opticaltelecommunication, it is preferable that most of the optical power isinjected into the optical fiber, while the system of using the feebleleakage light at the incident end of the optical fiber 142 issufficiently practical.

[0672]FIG. 88 shows another embodiment of the present invention.

[0673] Referring to FIG. 88, the monitoring photodetector 142P is formedbetween the surface emission laser diode chip 32 and the connectorsubstrate 151 in the vicinity of the incident end of the optical fiber142 facing the laser diode chip 32. Similar to FIG. 86, the laser diodes32, the optical fibers 142 and the photodetection devices 142P arearranged in a one-dimensional array, while the present invention is notlimited to such a specific case but is applicable also to the case inwhich there is formed a two-dimensional array on the mount substrate131. Similarly to the explanation above, each of the laser diodes isrepresented as a chip, while it is also possible to form a number oflaser diode emission parts 32A on a single chip 32 monolithically as alaser diode element. In view of simplicity of illustration, the drivercircuit and the laser output control circuit are not illustrated.

[0674] In the example of FIG. 88, the monitoring photodetector 142P isprovided between the substrate 131 and the connector substrate 151 inthe form supported on a support member 142W, contrary to the case ofFIG. 86.

[0675]FIG. 89 shows a further embodiment of the present invention.

[0676] Referring to FIG. 89, the monitoring photodetectors 142P aredisposed on the mount substrate 131 together with the surface-emissionlaser diode chip 32 and detects a part of the optical beam reflected bythe connector substrate 131. In this embodiment, too, it is possible toform a number of laser diode elements 32A in a laser diode chip 32 andform the photodetectors 142P also on the chip 32 monolithically adjacentto the laser diode elements 142P.

[0677] According to the latter construction, the laser diode elements32A and the photodetectors 142F are formed simultaneously and with highprecision. Further, the cost of assembling is reduced. In Figure 89,too, the illustration of the driver circuit of the laser diode 32 or theoutput control circuit is omitted for the sake of simplicity.

[0678] In the present embodiment, most of the laser beam emitted fromthe surface-emission laser diode 32 is injected into the optical fiber142 coupled optically to the laser diode 32. Thereby, the part of thelaser beam failed to enter the optical fiber 142 is reflected at thebottom surface of the connector substrate and enters the photodetectiondevice 142P. Thus, in the present embodiment, too, it is possible tocontrol the output of the laser diode 32 by using the leakage light atthe incident end of the optical fiber 142.

[0679] Next, another embodiment of the present invention will bedescribed with reference to FIG. 90.

[0680] Referring to FIG. 90, it can be seen that the relationshipbetween the laser diode 32 and the monitoring photodetector 142P is thesame as in the case of FIG. 89 except that there is provided a reflector151R at the bottom surface of the connector substrate 151 for improvingthe efficiency of reflection.

[0681] Such a reflector 151R can be formed by providing a metal film ofAl, Ag or Au on the bottom surface of the connector substrate 151 thatfaces the laser diode 32. In order to reflect the optical beam of longwavelength, it is preferable to use a metal film of Au.

[0682] In the present embodiment, too, it is possible to control thelaser output of the surface-emission laser diode by using a leakagelight which has failed to enter the optical fiber in the vicinity of theoptical fiber, similarly to the previous embodiments. As a result of theuse of reflector, the optical output control is achieved with improvedprecision with weaker power of the reflection light.

[0683] [Sixteenth Embodiment]

[0684] Next, a further embodiment will be described.

[0685]FIG. 91 shows an example of the optical telecommunication systemthat uses a long-wavelength laser diode of the present invention. Morespecificallyr FIG. 91 shows the construction in which the optical fiber72 extending out from the module package 71, in which the laser diodechip 32 is accommodated, is connected to the optical fiber 73 of theoptical telecommunication system. In FIG. 91, those parts correspondingto the parts described previously are designated by the same referencenumerals and the description thereof will be omitted.

[0686] Referring to FIG. 74, the optical fiber 72 drawn out from themodule package 71 is connected to the optical fiber 73 used for opticaltelecommunication at the optical connector 171. When there exists air atthe connection part, there arises a reflection of the optical beam inview of the difference of refractive index of the air with respect tothe refractive index of the optical fiber 72 or 73. In order to suppresssuch a fluctuation of refractive index a the optical fiber connectionpart, there are proposals to inject a refractive index is matcher in theform of a gel so as to suppress the fluctuation of the refractive indexor to achieve a complete attachment of the optical fibers (PC: physicalcontact). The present invention uses this PC technology for theconnection of the optical fibers.

[0687] As represented in FIG. 91, the optical fibers 72 and the opticalfibers 73 are held in the connector 171 respectively by a ferule 72F anda ferule 73F for preventing damaging of the optical fibers. The ferules72F and 73F are formed of a cylindrical body of a zirconia ceramic thathas a large mechanical strength. Thereby, the optical fibers areinserted into the central hollow part, and fixed therein by using anadhesive. Further, the ferules 72F and 73F are held in the opticalconnector 171 by a pair of split sleeves 172.

[0688]FIG. 92 shows the relationship between the optical fibers 72 and73, the ferules 72F and 73F and the split sleeve 172.

[0689] Referring to FIG. 92, the split sleeve 172 consists of a pair ofmembers formed of a copper bronze and having the shape of being splitfrom a hollow cylinder.

[0690] As represented in FIG. 92, a pair of split sleeve members 172holds the ferules 72F and is 73F, and the ferules 72F and 73F are urgedwith each other by respective springs 173A and 173B with a predeterminedforce. Thereby, there is formed the desired PC connection. In thepresent embodiment, it is possible to construct a rigid and highlyreliable optical connection.

[0691] Generally, a laser diode is provided with a safety standard forpreventing damages to human body. In the case of the surface-emissionlaser diode of 1.1-1.7 μm, it is possible to satisfy the safety standardwhile operating the laser diode with a large output power as comparedwith the laser diode having the oscillation wavelength in the visiblewavelength band (0.4-0.7 μ).

[0692] [Seventeenth Embodiment]

[0693] Next, another feature of the present invention will be describedof the coupling between the laser diode and optical fiber or laserdiode-and optical waveguide.

[0694] As represented in FIG. 93, the laser beam of the surface emissionlaser diode emitted perpendicularly to the substrate has a opticalintensity distribution generally close the Gauss distribution profile inthe plane perpendicular to the optical axis.

[0695] Assuming that the beam diameter is equal to the FWHM (full-widthhalf-height) value of the beam profile, it is possible to evaluate theemission angle θ of the optical beam from the beam diameter and thedistance between the laser diode and the detection surface.

[0696] As a result, it turned out that the emission angle θ of thesurface-emission laser diode of the present invention is generallysymmetric about the optical axis and takes a value of 5-10 degrees.

[0697] In contrast to this, conventional laser diode of theedge-emission type having the same oscillation wavelength of 1.1-1.7 μmhas a much larger emission angle θ and a very large aspect ratio.Typically, the optical emission angle θ⊥ has a value of about 35 degreesin the direction vertical to the plane of the substrate and the opticalemission angle θ// parallel to the place of the substrate takes thevalue of about 25 degrees. Thus, it has been necessary to use an opticalelement such as a microlens for realizing high efficiency opticalcoupling.

[0698] In contrast to this, in the case of the surface-emission laserdiode of the present invention, is the angle of optical emission θ isvery small as noted above, and the spreading of the optical beam isminimized even in the case there is a large distance between the laserdiode and the optical fiber or between the laser diode and the opticalwaveguide. Thereby, it becomes possible to eliminate the microlens,while the removal of the microlens provides an beneficial effect in thatthe distance between the laser diode and the optical fiber is reduced.Further, even in the case the distance between the laser diode and theoptical fiber or the laser diode and the optical waveguide is large, thespreading of the optical beam is small and an efficient optical couplingbecomes possible without providing an intervening lens.

[0699]FIG. 94 shows a schematic diagram with regard to spreading of thelaser bean in the laser diode 32 of the present invention and FIG. 95shows an example of calculation of beam spreading.

[0700] Referring to FIG. 94, the laser emission part 32A of the laserdiode 32 has an aperture size d [μm] and the laser beam is emitted fromthe laser emission part 32A with an emission angle θ. Further, there isprovided an edge surface of the optical beam 180 at the positionseparated from the laser diode 32 with an optical length 1 [μm]. Theoptical fiber 180 includes a core 181 having a diameter X [[μm] and acladding 182 surrounding the core, and the optical fiber 180 is providedso as to align the laser diode optically such that the optical axis ofthe optical fiber 180 and the optical axis of the laser diode coincidewith each other. Here, it should be noted that the diameter d of theaperture represents the diameter itself when the diameter has a circularshape, while in the case the diameter has a square shape, the diameter drepresents the length of one edge. Further, when the opening has othershape such as a rectangle, the diameter d represents the diameter of acircle having an area of an ellipse inscribing the rectangular opening.

[0701] The reason that the optical path length between the laser diodeand the optical fiber edge or optical waveguide edge is to include thecase of using a mirror for deflecting the optical beam to be describedlater with reference to FIG. 97. When there is no such a deflection ofthe optical path and the optical beam propagates straight, the opticalpath length from the laser diode to the optical fiber edge or theoptical waveguide edge becomes identical with the distance from thelaser diode to the optical fiber edge or the optical waveguide edge. Inthe case of an optical waveguide, it is general that the corecross-section is not a circle but a square or rectangle. Thus, in thecase of a square core, the edge size is set as X [μm], while in the caseof a rectangular core, the size of the shorter edge is defined as X[μm].

[0702] In FIG. 94, it can be seen that the beam size of the optical beamemitted from the laser diode perpendicularly to the epitaxial layerstherein, the beam diameter of the laser beam increases with the opticalpath length L and the optical emission angle θ until it reaches the edgesurface of the optical fiber or optical waveguide. Thereby, the beamsize at the optical fiber edge or the optical waveguide edge is given as

d+2l tan(θ/2).

[0703] Thus, when this beam size falls in the core diameter X of theoptical fiber or the optical waveguide, excellent optical coupling isachieved.

[0704] Based on the above equation, FIG. 95 shows the relationshipbetween the optical path length l and the beam diameter for the case ofthe aperture diameter of 5 μm and the optical emission angle of 10degrees, in comparison with the conventional case of an edge-emissiontype laser diode having an optical emission angle of 35 degrees.

[0705] Referring to FIG. 95, it can be seen that the spreading of thebeam diameter is substantially small as compared with the conventionalcase and that it is possible to coincide the core diameter X and thebeam diameter in the case a commonly used multimode optical fiber havinga core diameter of 50 μm (cladding diameter of 125 μm) is used for theoptical fiber, provided that the optical path length l is set to 260 μm.

[0706] As long as the optical path length l is smaller than theforegoing length in which the core diameter X coincide with the beamdiameter, it is possible to achieve an excellent optical coupling withlittle optical loss. From the result of FIG. 95, it is concluded thatthe optical alignment between the laser diode and the optical fiber oroptical waveguide is not critical in the axial direction in the case ofthe laser diode of the present invention, and a very coarse alignment issufficient for achieving the necessary optical coupling. In the case ofa plastic optical fiber having a core diameter of 100 μm is used, theoptical path length l in which the laser beam diameter coincides withthe core diameter increases further to 550 μm. Thereby, it is possibleto provide the optical fiber with a separation from the laser diodepackage.

[0707]FIG. 96 shows an example of coupling an optical fiber of anoptical telecommunication system with the surface-emission laser diodeof the present invention. In FIG. 96, those parts corresponding to theparts described previously are designated by the same reference numeralsand the description thereof will be omitted.

[0708] Referring to FIG. 96, the telecommunication system includes themount substrate 131 carrying thereon the surface-emission laser diodechip 32 in which the laser diodes 32A are formed as a two-dimensionalarray, and the mount substrate 131 further carriers a driver circuit ofthe laser diode not illustrated. Further, there are provided atwo-dimensional array of photodetectors (not shown) as well as thedriver circuit not illustrated cooperating with the photodetectors,wherein an optical fiber array including optical fibers 191 is providedon the laser diode chip 32 such that each of the optical fibers 191 facea corresponding laser diode 32A. It is also possible to use an opticalwaveguide array in place of the optical fiber array in the constructionof FIG. 96. Further, the optical telecommunication system of FIG. 96 maybe a bi-directional optical telecommunication system. In this case, theoptical transmission part and photodetection part are provided at bothends of the optical fibers.

[0709] Referring to FIG. 96, the mount substrate 131 is formed of athermally conductive Si substrate and the laser array chip 32 is mountedon the mount substrate 131. The laser array chip 32 may contain thelaser diode of FIG. 1 as a laser diode element constituting the array.In the illustrated example, the laser diodes having an oscillationwavelength of 1.3 μm is used, wherein each of the laser diodes 32A hasan aperture having the diameter of 10 μm for optical output. Twelvelaser diodes 32A are formed on the mount substrate 131 with a pitch of200 μm.

[0710] On the mount substrate 131, there is provided a hole array member191 having a number of penetrating holes with a pitch of 200 μm incorrespondence to the pitch of the laser diodes 32A on the chip 32,wherein each of the holes has a diameter of 125 μm in correspondence tothe diameter of the multimode optical fibers. The hole array member 191may be formed of AlN and carries a guide 191X in correspondence to amarker 32X provided on the laser diode chip 32. Thereby, the hole arraymember 191 is mounted on the laser diode chip 32 such that the guide191X coincides with the marker 32X. The hole array member 191 has anexcellent thermal conductivity of about 300 Wm⁻¹K⁻¹ and is used as aneffective heat radiation part when it is provide close to the laserdiode chip 32. Thereby, a stable optical telecommunication system isrealized by dissipating the heat associated with the laser oscillationefficiently.

[0711] In each of the penetrating holes of the hole array member 191, amultimode optical fiber 192 is inserted and the optical fiber is fixedtherein by an adhesive in the state that the optical fiber engages thelaser diode chip 32. With such a construction, it is possible to achievean exact alignment between the laser diode element 32A and the opticalfiber 1691 in the direction perpendicular to the optical axis direction.

[0712] As noted above, the optical fiber 191 is merely contacted withthe chip 32 and the accuracy of optical alignment in the axial directionis poor. There can be a case in which a space of 0-20 μm may be formedbetween the laser diode and the optical fiber. However, because of thevery small emission angle θ of the laser diode of 8 degrees in thepresent example, and in view of the large diameter d of 10 μm for thelaser diode 32A, the optical beam diameter is only 17 μm at the distanceof 50 μm from the surface of the laser diode chip 32. Thus, the beamdiameter is still much smaller than the core diameter of 50 μm for themultimode optical fiber 192, and excellent optical coupling ismaintained. Further, there is no need of providing a coupling lensbetween the laser diode 32A and the optical fiber 191.

[0713] In the experiment conducted on the construction of FIG. 96 inwhich the optical fiber 191 is pulled out gradually after beingcontacted with the laser diode chip 32 by using a micrometer, it wasconfirmed that the laser diameter becomes 66 μm when the distancebetween the laser diode and the optical fiber is 66 μm. In this case,the optical beam diameter is larger than the core diameter of themultimode optical fiber 191 and the foregoing relationship is failed.Thus, no sufficient optical coupling would be achieved in this case.

[0714] Table 7 below represents the experiments conducted by theinventor. TABLE 7 d + 21 tan (θ/2) [μm] X (μm) remarks 10 50 ◯ 20 50 ◯30 50 ◯ 40 50 ◯ 50 50 ◯ 60 50 Δ 70 50 X 80 50 X 10   62.5 ◯ 20   62.5 ◯30   62.5 ◯ 40   62.5 ◯ 50   62.5 ◯ 60   62.5 ◯ 70   62.5 X 80   62.5 X

[0715] From the result of above, it can be seen that a practical opticalcoupling cannot be achieved unless the core diameter × is larger thanthe term given as d+2l tan (θ/2), where θ is the emission angle of theoptical beam and l represents the optical path length from the laserdiode to the optical fiber, d represents the diameter of the laser diodeopening.

[0716] In the explanation above, it should be noted that the number ofthe optical fibers is not limited to 12 but there may be only oneoptical fiber or there may be 4, 8, 16 optical fibers. Further, thepresent invention is not limited to a multimode fiber 191 b but a singlemode optical fiber may also be used for long distance transmissionFurther, it is possible to use a plastic optical fiber (POF), which isadvantageous to construct a short distance, low const opticaltelecommunication system. In such a system, it is preferable to providean anti-reflection coating on the edge surface of the optical fiber. Inthe present embodiment, it is also possible to use Si or C or aluminaceramics for the hole array member 191. As the hole array member 191functions also as a heat radiation part, it is preferable to use amaterial having a high thermal conductivity.

[0717] [Eighteenth Embodiment]

[0718] Next, another feature of the present invention will be describedof the coupling between the laser diode and optical fiber or laser diodeand optical waveguide.

[0719] The construction of the present invention is similar to that ofFIG. 96 except that the lser diode chip 32 and the optical fiber arecontacted with each other and the distance between the laser diode chip32 and the optical fiber 191 or optical waveguide is set to almost zero.Here, the representation “contact” also includes a separation of 0-10 μmby taking into consideration of the error at the time of the assemblingprocess.

[0720] In the present embodiment, a Si substrate having good thermalconductivity is used for the mount substrate 131 and the laser arraychip 32 including an array of surface-emission laser diodes 32A ismounted on the mount substrate 131. The laser diode 32A used in thepresent embodiment has a laser oscillation length of 1.3 μm.

[0721] In the present embodiment, the diameter of the laser diode is setto 10 μm and 12 laser diodes 32A are formed with a pitch of 200 μm.

[0722] Next, the multimode optical fibers 192 are inserted into theholes in the hole array member 191 having the penetrating holes of 125μm diameter with the corresponding pitch of 200 μm. Thereby, the tipends of the optical fibers 192 are projected slightly from the holearray member 191 such that the tip end of the optical fiber makes anengagement with the laser array chip 32.

[0723] Next, the tip end part of the optical fiber is polished, and thetip end of the optical fibers is aligned at the side of the hole arraymember 191 that makes a contact with the laser diode chip 32. Afterthis, the marker X and the guide 191X are matched and the opticalalignment is achieved between each of the laser diodes 32A and thecorresponding optical fiber 192. The laser array chip 32 and the holearray member 191 are then fixed in this state, and the laser diode chip32A and the optical fiber 192 are coupled with each other.

[0724] According to the present embodiment, an optical coupling betterthan the previous embodiment is achieved. Thus, in the presentembodiment, there occurs little spreading of the optical beam and thelaser beam diameter is more or less coincident with the diameter d ofthe aperture forming the laser diode 32A. Thus, the diameter of thelaser beam is sufficiently smaller than the core diameter of the opticalfiber 191 and the alignment margin in the axial direction is increasedfurther. Thereby, it becomes possible to construct an optical systemusing a 1.3 μm surface emission laser diode with low cost.

[0725] [Nineteenth Embodiment]

[0726]FIGS. 97A and 97B are diagrams showing the coupling of the laserdiode and an optical wave guide according to another embodiment of thepresent invention, wherein FIG. 97A shows an oblique view while FIG. 97Bshows a cross-sectional view.

[0727] In the present embodiment, the laser beam emitted from a laserdiode 32A is deflected by a mirror 301. In FIGS. 80A and 80B, thoseparts corresponding to the parts described previously are designated bythe same reference numerals and the description thereof will be omitted.

[0728] Referring to FIGS. 97A and 97B, a Si substrate having anexcellent thermal conductivity is used for the mount substrate 131, andthe laser array chip 32 in which the laser diodes 32A are arranged inthe form of an array is mounted on the mount substrate 131. In thepresent embodiment, each of the laser diodes 32A has an aperture with adiameter of 15 μm, and four laser diodes 32A are formed.

[0729] In this embodiment, another mount substrate 131A is provided inwhich a mirror 301 is formed by mounting a reflecting member or forminga reflecting layer monolithically. Further, an optical waveguide 302 isformed on the mount substrate 131A. For example, the mirror 301 may beformed by applying an anisotropic etching to the Si substrate by using aKOH etchant and by providing an Ag film on the crystal surface formed asa result of the anisotropic etching.

[0730] In the present embodiment, an optical waveguide 302 is formed onthe mount substrate 131A. The optical waveguide 302 is formed bydepositing a lower cladding layer 302A, followed by depositing a spolymethacrylate (PMMA), followed further with a patterning process toform a core pattern 302B. Typically, the core pattern 302B has a crosssectional form of 50×50 μm. Other than PMMA, the optical waveguide layermay be formed also by polyimide or epoxy resin or polyurethane orpolyethylene Further, it is also possible to form an inorganic film suchas silicon oxide film. Further, these organic films may be formed by aspin-coating process of dip-coating process in combination with apatterning process. Further, it is possible to form the opticalwaveguide by a resin molding process or molding process.

[0731] In the present embodiment, the mount substrate 131 and the mountsubstrate 131A carrying the optical waveguide 302 are fixed such thatthe optical axis of the laser diode 32A and the optical axis of theoptical waveguide 302 become coincident.

[0732] In the experiments conducted by the inventor, a laser diodehaving an aperture of 15 μm diameter and the optical emission angle θ of10 degrees is used, and the optical path length l between the laserdiode 32A and the optical waveguide 302 is changed by setting theposition of the end surface of the optical waveguide 302 to 50 μm, 100μm and 250 μm As a result, it was confirmed that an excellent result isobtained in the case the optical path length is 50 μm and 100 μm, whileno satisfactory optical coupling was achieved in the case the opticalpath length is set to 250 μm.

[0733] Anyway, the present embodiment can eliminate the lens and only acoarse optical alignment is sufficient for the axial direction Thus, byusing a surface-emission laser diode of 1.2 μm, it becomes possible toconstruct an optical alignment having a tolerance with regard to theoptical alignment in the axial direction or the direction of the opticalaxis.

[0734] In the present embodiment, the mirror 301 is formed separately tothe optical waveguide 302. On the other hand, it is possible to form a45 degree. surface at the end of the optical waveguide 302 by a dicingblade, and the like, and by depositing a metal film such as Ag on suchan oblique surface. Thereby, a mirror integral with the opticalwaveguide 302 is formed.

[0735] In the present embodiment, the diameter of the optical waveguideis set to 50 μm in correspondence to core diameter of the multimodeoptical fiber. In the case a single mode optical fiber is used, thediameter of the optical waveguide has to be set to about 10 μm. In thiscase, too, the same fundamental equation holds. Further, it should benoted that the cross sectional form of the core pattern 302B in theoptical waveguide 302 is not limited to the square pattern but arectangular pattern may also be used. Further, it is possible totransmit plural optical signals in a single optical waveguide as in thecase of an optical sheet.

[0736] [Twentieth Embodiments]

[0737]FIG. 98 shows the construction of coupling the laser diode chip 32with the optical waveguide 302 according to another embodiment of thepresent invention.

[0738] Referring to FIG. 98, a Si substrate having excellent thermalconductivity is used for the mount substrate 310 and the laser diodechip 32 carrying the laser diodes 32A of the structure of FIG. 1 ismounted on the substrate 310. In the present embodiment, too, asurface-emission laser diode having an oscillation wavelength of 1.3 μmis used for the laser diode 32A. The laser diode used in the presetembodiment has the aperture diameter d of 7 μm and the optical emissionangle θ of 8 degrees. In the present embodiment, the laser diode 32A isused as a single device, not in the form of array.

[0739] The mount substrate 310 carrying thereon the laser diode chip 32is fixed on a package body 311 with positioning. Further, the opticalaxis of the laser diode 32 is aligned with the optical axis of thesingle mode optical fiber 313 held on an optical fiber guide 312, byaligning the optical fiber guide 312 and the package 311 in advance byusing a guide 311A on the package body 311 and a guide pin 312A on theoptical guide 312.

[0740] The single mode optical fiber 313 includes a core 313A having adiameter of 10 μm and a clad having a diameter of 125 μm and surroundingthe core 313A, wherein the diameter of the optical fiber guide 312 isset so as to coincide with the outer diameter of the cladding of theoptical fiber 313.

[0741] In the construction of the present embodiment, an excellentoptical coupling is achieved by contacting the single mode optical fiber313 to the laser diode 32. Further, the present invention enables abroadband optical signal transmission by using the single mode opticalfiber 313 over a long distance. Thus, according to the presentembodiment, it became possible to construct an optical telecommunicationsystem having excellent optical coupling by using the surface-emissionlaser diode of the 1.3 μm band.

[0742] [Twenty-First Embodiment]

[0743] Next, another embodiment of the present invention will bedescribed.

[0744]FIG. 99 shows an example of the optical telecommunication systemthat uses a long-wavelength laser diode according to another embodimentof the present invention.

[0745] Referring to FIG. 99, the optical transmission system includes asurface-emission laser diode 32 having the emission part 32A and anoptical fiber 352, wherein the laser diode 351 and the optical fiber 352are coupled directly at the laser emission part 32A. of course, it ispossible to achieve the optical coupling by using a lens.

[0746] Assuming that the laser emission part 32A of the surface-missionlaser diode 32 is d and the core diameter of the optical fiber 312 as F,it can be seen that the laser beam from the laser diode 32 diverges asrepresented in FIG. 99 by a broken line 351B. In FIG. 99, it should benoted that d represents the diameter of the circle inscribing thepolygonal laser emission part 32A. In this case, the emission angle ofthe laser beam is much smaller than the case of a conventionaledge-emission laser diode. Thus, in the case the laser diode 32 isprovided near the optical fiber, it should be noted that a high opticalcoupling can be achieved when the optical axis of the laser diode isperpendicular to the optical fiber end surface and is coincident withthe optical axis of the laser diode, and the aperture diameter of thelaser diode is equal to or smaller than the core diameter.

[0747] As noted before, the surface-emission laser diode used in thepresent embodiment operates in the wavelength band of 1.1-1.7 μm, and along distance transmission becomes possible by using the wavelength bandof 1.3-1.55 μm due to the small optical loss of the quartz optical fiberin this wavelength band.

[0748] Assuming that the laser emission part 32A of the laser diode 32has the diameter of d (in the case the laser emission part 32A has apolygonal shape, the diameter d is the diameter of a circle inscribingthe polygonal laser emission part 32A, it is possible to increase theoptical coupling efficiency by setting the foregoing parameters F and dso as to satisfy the relationship of

F/d≦2  (2)

[0749] In the embodiment of FIG. 99, it should be noted that the laseremission part 32A and the optical fiber 352 are coupled directly and nolens is interposed.

[0750] In the conventional optical system that uses an edge emissiontype laser diode of the 1.3 μm band, there is been a poor opticalcoupling efficiency between the laser diode and the optical fiber, andit has been difficult to couple these directly. Further, the return beamincident to the laser dude from the optical beam in the backwarddirection has caused a change oscillation state of the laser diode.

[0751] In the case of the present invention, the laser diode is asurface-emission laser diode and operates in the long-wavelength band.Thus, the laser diode has a generally circular beam shape characterizedby excellent aspect ratio close to 1. Thereby, the efficiency of thelaser diode is improved substantially as compared with the case of theedge-emission type laser diode.

[0752] Further, the laser diode of the present invention has thereflector of very high reflectance and the effect of the return beam issuccessfully suppressed. Thereby, it becomes possible to couple thelaser diode and optical fiber directly, and the optical isolator used inthe conventional optical telecommunication system can be eliminated.

[0753] Designating the diameter of the laser emission part 32A as d andthe optical fiber core diameter as F, it is possible to increase theoptical coupling efficiency by setting the parameters d and F so as tosatisfy the relationship

0.5≦F/d≦2  (3)

[0754] Hereinafter, the reason of this will be explained with referenceto Table 8, which summarizes the result of the study of the inventor ofthe present invention on the optical coupling loss. TABLE 8 F/d couplingloss (dB) performance 0.4 >5 X 0.5 3-5 ◯  0.65  1 ◯ 2.0 3-5 ◯ 2.2 >5 X

[0755] Referring to Table 8, it can be seen that the efficiency ofoptical coupling is decreased when the diameter d of the beam emissionpart 32A has exceeded the core diameter F. On the other hand, it can beseen also that as long as there is a relationship d≦2F (in other words0.5>F/d), the optical coupling loss can be suppressed within 3-5 dB. Inthe case the diameter d of the beam emission part 32A is smaller thanthe core diameter, a highly efficient optical coupling is achieved inthe case the emission angle of the laser diode, determined by thediameter of the circle inscribing the beam emission part 32A and thewavelength, is smaller than the numerical aperture NA for allowing asingle mode optical coupling to a single mode optical fiber.

[0756] For example, in the case the core diameter is set to 10 μm andthe core refractive index is 1.4469 and the clad refractive index if1.4435, the numerical aperture NA that enables single mode opticalcoupling becomes 0.0995 at the wavelength of 1.3 μm The diameter d ofthe beam emission part 32A corresponding to this is about 6.5 μm.

[0757] On the other hand, even in the case the diameter of the beamemission part 32A is less than 6.5 μm, it is possible to suppress theoptical coupling loss to the level of 3-5 dB when the diameter of thebeam emission part 32A is about 5 μm. From this, it is concluded that itis preferable to choose the parameters F and d to satisfy therelationship

0.5≦F/d≦2.

[0758] While the foregoing arguments have been for the case of using asingle mode optical fiber, the foregoing condition is applicable also tothe case of using a multimode optical fiber coupling a single modeoptical fiber via a tapered optical waveguide.

[0759] Next, another example of the optical telecommunication system ofthe present invention will be described with reference to FIG. 100.

[0760] Referring to FIG. 100, the present embodiment uses a couplinglens 353 between the surface-emission laser diode 32 and the single-modeoptical fiber. The lens 353 may be formed of a single lens or a lenssystem in which a plurality of lenses are combined. In the case ofconstructing the lens 353 by a single lens, it is preferable to disposethe lens 353 close to the beam emission part 32A of the laser diode chip32.

[0761] In the construction of FIG. 100, it becomes possible to suppressthe optical coupling loss effectively even in the case the diameter d ofthe beam emission part 32A is set larger than the core diameter of theoptical fiber 353, by appropriately choosing the lens power of thecoupling lens 353.

[0762] In the case the core diameter is 10 μm and the diameter d of theemission part 32A is 20 μm, for example, the beam size is reduced by ½by the lens 353. Thus, designating the focal distance of the lens 353 asf, the laser wavelength as λ, the radius of the beam emission part 32Aas ω0 (=10 μm) and the refractive index as n, the focal distance f isobtained by the relationship$\frac{\frac{\lambda \quad f}{\pi \quad \omega_{0}^{2}n}}{{\sqrt{1 + \left\lbrack {1 + \frac{\lambda \quad f}{{\pi\omega}_{0}^{2}n}} \right\rbrack}}^{2}} = \frac{5}{10}$

[0763] In this case, the focal distance f becomes about 140 μm.

[0764] In the case of using a coupling lens, it is possible to achievean efficient optical coupling when there holds a relationship betweenthe parameters d and f noted before as

d≧f, or

F/d≦1.  (4)

[0765] Further reference should be made to Table 9 below. TABLE 9 F/dcoupling loss (dB) performance 1.2 >5 X 1.0 3-5 ◯ 0.8  1 ◯

[0766] In the embodiment of FIG. 100, the coupling lens 353 was providedby a single lens. On the other hand, it is possible to construct thelens 353 by a plurality of lenses. For example, as represented in FIG.101, the lens 353 may be formed of two lenses 353A and 353B.

[0767] Referring to FIG. 101, the diverging beam from the beam emissionpart 32A is focused by the first lens 353A to the second lens 353B, andthere is formed a beam waist at the plane of the second lens 353B. Thelens 353B functions as the lens 353 of FIG. 100 According to the presentembodiment, it becomes possible to maintain a high coupling efficiencyin the case a single lens cannot be disposed near the beam emission partof the laser diode or in the case the divergence of the beam isexcessive and the optical coupling efficiency is decreased, byconstructing the lens 353 by plural lenses.

[0768] In the description heretofore, it was assumed that a single modeoptical fiber is used for the optical fiber 352. On the other hand asimilar effect is achieved also in the case of using a multimode opticalfiber or a tapered optical waveguide, as long as the relationship ofEquation (4) is satisfied.

[0769] In the construction that uses a conventional edge-emission laserdiode, there is a possibility that the laser oscillation is influencedby the return beam from the coupling lens, and it has been necessary toprovide an optical isolator. In the case of the surface-emission laserdiode, there is provided a reflector structure of high reflectance andthe effect of the return beam is successfully eliminated. Thus, itbecomes possible to eliminate the optical isolator.

[0770] Next, another embodiment constructed by a surface-emission laserdiode and the optical fiber will be explained with reference to FIG.102.

[0771] Referring to FIG. 102, the laser diode chip 32 includes aplurality of beam emission parts 32A arranged in the form of array. Ofcourse, it is possible to dispose the laser diode chips 32 themselves inthe form of array. Further, a plurality of laser diode chips may bearranged in the form of array.

[0772] In FIG. 102, the optical fiber is coupled directly to thecorresponding optical emission part 32A, and thus, it is possible tosatisfy the Equation (3) explained before with reference to FIG. 99.Thereby, it becomes possible to construct an optical telecommunicationsystem of large capacity.

[0773]FIG. 103 is an embodiment in which a coupling lens is providedfurther to the construction of FIG. 102. In the construction of FIG.102, too, the relationship between the beam emission part 32A, the lensarray and the optical fiber 352 is the same as in the case of FIG. 102.Thus, by satisfying the Equation (4) by choosing the parameters d and F,an efficient optical coupling becomes possible As the beam emission part32A is arranged in the form of array, an optical telecommunicationsystem of large capacity is realized. In the present embodiment, it ispossible to combine a plurality of lenses in each of the coupling lens355.

[0774] Twenty-Second Embodiment]

[0775] Next, another embodiment of the present invention will bedescribed.

[0776]FIGS. 104A and 104B show an example of the opticaltelecommunication system that uses a long-wavelength laser diode of thepresent invention as an optical source and shows the state in which thelaser diode chip 32 carrying the beam emission part 32A is connectedwith a laser driver IC 32D including a CMOS circuit, wherein FIG. 104Ashows a side view while FIG. 104B shows a plan view.

[0777] Referring to FIGS. 104Aa and 104N, the laser diode chip 32 andthe laser driver IC 32D are mounted on a conductive submount 401 by aconductive adhesive. Further, the laser diode chip and the laser driverIC 32D are connected by a high-frequency transmission line 402(microstrip line in the present embodiment), and each chip 32 isconnected to this microstrip line 402 by way of a bonding wire 403.

[0778] In the case of the surface-emission laser diode for opticaltelecommunication, it is necessary to carry out a very fast modulationin the order of several hundred MHz to several GHz. Thus, it ispreferable to decrease the distance between the laser diode chip 32 andthe laser driver IC 32D. On the other hand, there can be a case in whichsuch a construction is not possible because of the layout of the opticalsystem. When an ordinary wiring is used in such a case for connectingthe laser diode chip 32 and the laser driver IC 32D, however, therearise s problem of electromagnetic emission from such wiring. In thepresent embodiment, the laser diode chip 32 and the laser driver IC 32Dare connected such that there occurs no such electromagnetic radiation.

[0779] By using such a construction, no electromagnetic emission occursfrom the wiring part and the need of providing special shielding meansis eliminated. Thereby, the cost of the optical telecommunication systemis reduced.

[0780] In the present embodiment, a microstrip line was used for thehigh-frequency transmission line 402. However, any of unbalancedtransmission line such as coplanar transmission line or triplate linemay be used. Further, the connection between the laser diode chip 32 andthe laser driver IC 32D is not limited to the bonding wired butflip-chip wiring or TAB bonding or microbump bondin may be used.

[0781] [Twenty-Third Emodiment]

[0782] In the embodiment of FIG. 52, a system that uses asurface-emission laser diode of long-wavelength band of 1.1-1.7 μm hasbeen explained. Conventionally, an optical telecommunication using thewavelength band of 0.85 μm band is studied. However, in this wavelengthband, the optical transmission loss is large in the optical fiber andpractical use of such a system was not successful. Further, there hasbeen no stable laser diode device in the long wavelength band in whichthe optical transmission loss is small. in the present invention, on theother hand, it became possible to construct a surface-emission laserdiode operable in the wavelength band of 1.1-1.7 μm by improving thesemiconductor distributed Bragg reflectors 12 and 18 and by providingthe non-optical recombination elimination layers 13 and 17, such thatthe laser diode operates stably at low power. Thereby, a practicaloptical telecommunication system has become the matter of reality.

[0783] In the example of FIG. 52, the optical telecommunication systemis formed of the long-wavelength surface-emission laser diode chip, thefirst optical fiber FG1 injected with the laser beam emitted from thebeam emission part 32A in the chip 32 and acting as an opticaltransmission path, a second optical fiber FG2 injected with the laserbeam transmitted through the first optical fiber FG1 and functioning asan optical transmission path, a third optical fiber FG3 injected withthe laser beam transmitted through the optical fiber FG2 and functioningas an optical waveguide, and a photodetector chip 34 including aphotodetection part 34A coupled optically to the optical fiber FG3 fordetecting the laser beam transmitted through he optical fiber FG3.

[0784] Further, the optical connection module MG1 is provided betweenthe laser diode chip 32 and the first optical fiber FG1, while theoptical connection module MG2 is provided between the optical fiber FG1and FG2. Similarly, the optical connection module MG3 and FG4 areprovided between the optical fibers FG2 and FG3 and between the opticalfiber FG3 and the photodetector 34.

[0785] In the example of FIG. 52, the first optical fiber FG1 is coupleddirectly to the beam emission part 32A of the laser diode chip 34without intervening an optical system.

[0786] With reference to FIG. 94, a description was made on therelationship that is required between the laser diode of the presentinvention and the optical fiber.

[0787] In the long-wavelength surface-emission laser diode of thepresent invention, the optical emission angle of the laser beam is about10 degrees, and the laser diode is use din combination with an opticalfiber which may have a core diameter of 50 μm (clad diameter of 125 μm).

[0788] In such a combination of the laser diode and the optical fiber,the bean emission part 32A may have a size of 0.005 mm×0.005 mm−0.002mm×0.002 mm. In terms of area S, these are represented as 0.000025mm²-0.0001 mm². In this case, it is possible to achieve excellentoptical coupling without the need of providing an intervening opticalsystem. Further, the same result holds also in the case an opticalwaveguide is used in place of an optical fiber.

[0789] In the present invention, the beam emission part 32 is tuned tothe wavelength of 1.1-1.7 μm, while the foregoing wavelength band isrelated to the operational voltage of the laser diode.

[0790] Thus, in the present embodiment, a detailed analysis wasconducted on the operational voltage of the laser diode 32 suitable forrealizing continues oscillation, not just a pulse oscillation.

[0791] Table 10 shows the experimental results of the presentembodiments. TABLE 10 emission area size S voltage No. (mm × mm) (mm2) VV/s remarks  1 0.005 × 0.005 0.000025 0.2  8000 X  2 0.005 × 0.0050.000025 0.3 12000 X  3 0.005 × 0.005 0.000025 0.375 15000 ◯  4 0.005 ×0.005 0.000025 0.4 16000 ◯  5 0.005 × 0.005 0.000025 0.5 20000 ◯  60.005 × 0.005 0.000025 0.6 24000 ◯  7 0.005 × 0.005 0.000025 0.75 30000◯  8 0.005 × 0.005 0.000025 0.9 36000 X  9 0.005 × 0.005 0.000025 1.248000 X 10 0.01 × 0.01 0.0001 1.2 12000 X 11 0.01 × 0.01 0.0001 1.313000 X 12 0.01 × 0.01 0.0001 1.5 15000 ◯ 13 0.01 × 0.01 0.0001 1.717000 ◯ 14 0.01 × 0.01 0.0001 1.9 19000 ◯ 15 0.01 × 0.01 0.0001 2.121000 ◯ 16 0.01 × 0.01 0.0001 2.3 23000 ◯ 17 0.01 × 0.01 0.0001 2.525000 ◯ 18 0.01 × 0.01 0.0001 3 30000 ◯ 19 0.01 × 0.01 0.0001 4 40000 X20 0.01 × 0.01 0.0005 5 50000 X 21 0.02 × 0.02 0.0004 2  5000 X 22 0.02× 0.02 0.0004 4 10000 X 23 0.02 × 0.02 0.0004 6 15000 ◯ 24 0.02 × 0.020.00041 8 20000 ◯ 25 0.02 × 0.02 0.0004 10 25000 ◯ 26 0.02 × 0.02 0.000012 30000 ◯ 27 0.02 × 0.02 0.00004 15 37500 X 28 0.02 × 0.02 0.00004 2050000 X

[0792] From the results above, it can be seen that, choosing theoperational voltage S such that the ratio of the operational voltage Vto the area S of the beam emission part 32A of the laser diode (V/S)falls in the range of 15000-3000, it can be possible to drive the laserdiode without causing a damage in the laser diode and the laser diodecan be operated continuously. By choosing the drive conduction as such,it is possible to realize a stable optical transmission system havingalong lifetime.

[0793] [Twenty-Fourth Embodiment]

[0794] Next, a further embodiment of the present invention will beexplained.

[0795]FIG. 105 shows the construction of an optical telecommunicationsystem using the long-wavelength laser diode according to the presentinvention, wherein those parts corresponding to the parts describedpreviously are designated by the same reference numerals and thedescription thereof will be omitted.

[0796] Referring to FIG. 105, the optical telecommunication system ofthe present invention has a construction to divide the optical output ofthe laser diode 32A provided on a mount substrate 301 into an opticalbeam for optical telecommunication and a monitoring beam by using themirror 301 provided on the mount substrate 301A, wherein the monitoringbeam thus divided is detected by the monitoring photodetector 142Pprovided on the mount substrate 301A. The monitoring photodetector 142Pcorresponds to the monitoring photodetector 142P explained previouslywith reference to FIG. 86. In FIG. 105, as well as in FIGS. 107 and 108to be described laser, there are formed a laser diode array by the laserdiodes arranged in the direction perpendicular to the plane of thedrawing. In correspondence to this, there are provided a plurality ofoptical waveguides.

[0797] The optical telecommunication system of the present embodiment isformed of an optical transmission part including the surface-emissionlaser diode 32 and the driver circuit thereof, the photodetection partincluding the planar photodetection unit and a drive circuit thereof,and an optical fiber or optical waveguide providing an opticaltransmission path extending between the optical transmission part andthe optical reception part. Although the driver circuit of the laserdiode 32 or photodetector 34 is not shown, these can be formed on thesubstrate of the respective devices. Alternatively, these can be formedintegrally with the laser diode device in the device fabricationprocess. By providing such an optical transmission part and opticalreception part at both ends of the optical transmission path, it becomespossible to realize a bi-directional optical telecommunication system.

[0798] As represented in FIG. 105, the laser beam emitted from a surfaceof the long-wavelength laser diode is divided by the mirror 301 and oneof the optical beams thus divided is then directed to the opticalwaveguide 302 provided with an optical alignment. This optical waveguide302 may be an optical fiber.

[0799] On the other hand, the other optical beam divided by the mirror301 is directed to the monitoring photodetection device 34 provided onthe mount substrate 301A. Thus, the mirror 301 is used to divide out thelaser beam to be supplied to the monitoring photodetector 34 and it ispreferable that such a mentoring optical beam is as weak as possiblewithin the range that a proper control of the laser diode is possible byusing such a monitoring device. In view of the power consumption of theoptical telecommunication system, it is preferable to provide as muchenergy as possible to the optical waveguide 302 as an optical signal.

[0800] Thus, in the present invention, the thickness of the metal filmof Au or Ag or Al used for the mirror 301 such that the transmittance ofthe mirror 301 is controlled for the wavelength of 1.1-1.7 μm. Further,it is also possible to provide openings of various shaped in the form ofgrooves, circles, squares, and the like, so as to control thetransmittance of the mirror 301. Thereby, in order to avoid the effectof unwanted optical interference, it is preferable to change the pitchor size or location of the openings at random. Further, it is possiblecontrol the transmittance of the mirror 301 by using a dielectricmultilayer mirror or semiconductor layered mirror.

[0801] As compared with the conventional laser diode of edge-emissiontype, the surface-emission laser diode used in the opticaltelecommunication system of the present invention has an advantageousfeature of small output dependence on temperature and little degradationwith time. While the laser diode of the present invention has suchadvantageous features, it is nevertheless preferable to control theoutput thereof by way of feedback control.

[0802] In the case of a conventional edge-emission laser diode, such amonitoring of the optical power of the laser diode was made easily bymonitoring the laser beam emitted from the rear edge surface of thelaser diode. In the case of the surface-emission laser diode, the laseroutput is obtained only at one side of the laser diode. Thus, theconstruction of monitoring the laser beam emitted in the backwarddirection cannot be used in the present invention. Further, the laserdiode ahs a relatively narrow angle of optical emission of about 10degrees. Thus, while there is a possibility of provide the laser diodeclose to the optical fiber or optical waveguide, there is no room at allfor inserting a monitoring photodetector between the laser diode and theoptical fiber.

[0803] On the other hand, the present invention provides an effective ansimple means of obtaining a monitoring laser diode by providing themirror 301 as noted above. Thereby, the output of the laser diode ismonitored with out increasing the optical path, and the output of thelaser diode is controlled positively and exactly. As the presentinvention uses the mirror 301 for deflecting the output optical beam ofthe laser diode, the optical axis of the reflected signal optical beambecomes parallel to the optical axis of the optical fiber, and thus, itbecomes possible to fix the optical fiber or optical waveguide on aplane parallel to the plane of the optical module and the opticalwaveguide 302 or optical fiber is fixed easily. Thereby, the obtainedstructure has an improved rigidity. Further, it is also possible toprovide a lens before or after the mirror 301.

[0804] Although not illustrated, it is possible to use a plurality oflaser diodes and corresponding optical waveguides or optical fibers. Inthis case, the laser diodes are arranged in a direction perpendicular tothe sheet of the drawing, and the mirror 301 extending also in thedirection perpendicular to the sheet of the drawing is used commonly bythe laser diodes forming the array.

[0805]FIG. 106 shows the block diagram of the feedback circuit thatcontrols the output of the laser diode 32 by using the divided laserbeam.

[0806] Referring to FIG. 106, the laser diode 32 is driven by a drivercircuit 161 corresponding the driver circuit 161 explained previouslywith reference to FIG. 87, and a part of the laser beam produced by thelaser diode 32 is provided to the monitoring photodetector 142P. Themonitoring photodetector 142P detects the output of the laser beam thussupplied and produces an electric output current indicative of theoutput of the laser diode 32. Further, the laser control part 162controls the laser diode 32 such that the output of the laser diode ismaintained constant.

[0807] In the construction of FIG. 106, it should be noted that thelaser diode 32 can be driven with a low drive voltage. Thereby, ordinaryCMOS circuit can be used for the driver circuit 161. Thereby, powerconsumption of the laser diode is reduced. As the wavelength band to bedetected by the monitoring photodetector 142P is in the range of 1.1-1.7μm, it is possible to use a photodiode of the InGaAs system. Further, inview of the gradual change of the output of the laser diode, it is notnecessary that the photodetector 142P has a high response speed. Thus,it is possible to use a high-sensitivity photodetector while sacrificingthe response speed.

[0808] Referring back to FIG. 106, there is formed a laser diode arrayincluding four laser diodes 32A each having the construction of FIG. 1,and the laser diode array is mounted on the mount substrate 301 of Sitogether with the drive circuit and the laser control circuit notillustrated. The laser diodes 32A has the wavelength of 1.3 μcm and maybe disposed on a single chip 32 with the pitch of 200 μm.

[0809] Next, the mirror 301 is formed by using a heat conductive Sisubstrate, which is transparent to the wavelength of 1.3 μm. By usingthe Si substrate for the mount substrate 301A, it is possible to formthe mirror easily by conducting an anisotropic etching process. Thereby,a crystal surface determined with respect to the principal surface ofthe substrate 301A is formed with exact angle. The etching process maybe conducted by using an etchant such as KOH. With this, a mirrorsurface having a 45 degrees is formed. Further, an Au deposition isconducted on the mirror surface 301, and the optical waveguide 302 isformed. In such a process, it is possible to control the transmittanceof the mirror 301 by controlling the thickens of the Au film.

[0810] In the formation of the optical waveguide 302, it should be notedthat a PMMA film is formed as the core layer after the cladding layer302A is formed. By patterning the core layer thus formed, the corepattern 302B is formed. Further, the upper cladding layer 302C is formedso as to cover the core layer 302B.

[0811] In the present embodiment, the core pattern 302B is patterned soas to form a cross section of 50×50 μm. The optical waveguide layer 302thus formed is coupled with the optical fiber not illustrated, and longdistance optical telecommunication system is constructed.

[0812] For the optical waveguide layer 302, it is possible to usevarious resins such as polyimide, epoxy resin, polyurethane orpolyethylene, in addition to PMMA. Further, it is possible to provide aninorganic film such as silicon oxide film. Further, the formation of theoptical waveguide layer 302 can be made by combining the spin coatingprocess or dip coating process and a patterning process. Alternatively,it is possible to form the optical waveguide by a resin molding; processor molding process.

[0813] Further, the optical axis of the laser diode is set coincidentwith the optical axis of the optical waveguide, and the mount substrates301 and 301A are fixed. Further, a planar photodiode is mounted on themount substrate 301A in optical alignment with the laser beam divided bythe mirror 301 as the monitoring photodetector 142P. A photodiode havingan optical absorption layer of InGaAs on the InP substrate may be usedof this purpose.

[0814] Further, the output of the photodetection device 142P isconnected to the laser control unit 162 by a wire bonding process Withthis, the feedback control circuit explained with reference to FIG. 106is obtained.

[0815] Table 11 below shows the result of evaluation of the opticaltransmission unit conducted external temperature. TABLE 11 mirrortransmissivitgy (%) remarks 0.1 X 0.2 X 0.3 X 0.5 Δ 0.7 Δ 1.0 ◯ 2.0 ◯5.0 ◯ 10   ◯ 20   ◯ 30   ◯ 40   ◯ 50   ◯ 60   Δ 70   X

[0816] In the experiment, the temperature is changed from 0-70° C. withthe step of 10° C., wherein Table 11 shows only the result of 20° C., asthe results for other temperatures were more or less the same as theresult of 20° C.

[0817] Referring to Table 11, it can be sent that an optical power of 10μW is detected by the monitoring photodetector 142P when the mirrortransmissivity is less than 1% for the optical power of mW level, whichis used commonly for optical telecommunication. As the change of theoptical power of the laser diode is smaller than this, no sufficientoptical energy needed for the control of the laser diode is supplied tothe photodetection device, and as a result, there is a fluctuation ofoptical output in the laser diode.

[0818] When the transmissivity exceeds 50%, on the other hand, too muchenergy of the laser output is used for controlling the output power ofthe laser diode. Thus, there occurs decrease of efficiency of theoptical telecommunication system From the result of Table 11, it can seseen that the transmissivity of 2% or more but 30% or less is preferablefor the mirror 301. By using such a construction, it is possible torealize an optical transmission unit capable of controlling the laseroutput stably. Thereby, it is preferable that the transmissivity of themirror 301 is in the range of or more but 50% or less, more preferably2% or more but 30% or less.

[0819] In the present embodiment, 4 laser diodes were used in the formof array. Of course, the number of the laser diode may be one, or thelaser diode may be used in the form of array including 8, 12, 16 or morelaser elements.

[0820] It is also possible to use an optical fiber for transmitting theoptical signals in place of the optical waveguide 301. When transmittinglarge amount of information over a long distance, the use of single modeoptical fiber is suited. In the case of transmitting information forshort distance with low cost, the use of plastic optical fiber (POF) issuitable. Further, there may be a possibility of using a multimodeoptical fiber in the intermediate applications.

[0821]FIG. 90 shows another embodiment of the present invention in whichthe electrode of the photodetection device is used for the mirror.

[0822] In the present embodiment, the long-wavelength laser diode 32 ofFIG. 1 is mounted on the Si mount substrate together with a drivercircuit and a laser control circuit not illustrated. In the presentembodiment, a laser diode having a laser oscillation wavelength of 1.2μm is used.

[0823] Similarly to the previous embodiments, a photodetector using aGaAsP material is used for the monitoring photodetector 142. In thepresent embodiment, the p-type electrode of the optical detectionsurface is used for the mirror 301.

[0824] More specifically, an Au film having a thickness of 300 nm andnot allowing passage of the 1.2 μm wavelength radiation is provided onthe photodiode as the electrode, and circular openings having variousdiameters in the range of 0.7-5 μm are formed. With this, atransmissivity of 5% is realized.

[0825] The photodiode 142P thus formed is mounted with an angle of 45degree with regard to the laser diode 32, and the output of thephotodiode 142P is connected to the laser control unit 162 electrically.Thereby, there is formed a feedback control system of the laser diodesimilar to the one shown in FIG. 106.

[0826] By providing a multimode optical fiber 302F having a core 302 fof 50 μm diameter and a clad of 125 μm diameter in optical alignmentwith the laser beam reelected by the mirror 301, an opticaltelecommunication system is constructed. Such an opticaltelecommunication system is simple in construction with reduced numberof parts, and it is possible to provide a compact optical transmissionmodule. Such an optical transmission module can control the laser outputstably and a reliable optical telecommunication is realized. In thepresent embodiment, it is also possible to form the mirror 301 on thesurface of the monitoring photodetection device separately to theelectrode.

[0827] Next, another embodiment of the present invention will beexplained with reference to FIG. 108.

[0828] Referring to FIG. 108, the present embodiment provides thelong-wavelength surface-emission laser diode 32 mounted on the Si mountsubstrate 301 together with the driver circuit and laser control circuitnot illustrated. In the illustrated example, four laser diodes 32A arearranged with the pitch of 200 μm, wherein each of the laser diodes hasa laser oscillation wavelength of 1.3 μm.

[0829] In the present embodiment, the edge of the optical waveguide iscut to form a 45 degree angle by a diamond blade, and the mirror 301 isformed by covering the oblique surface thus formed by an Au film.Thereby, the thickness of the Au film is controlled such that the Aufilm has a transmissivity of 3%. The optical waveguide 302 thusprocessed is coupled optically with the laser diode 32 by achievingoptical alignment, and the monitoring photodetector 142P is mounted onthe optical path of the optical beam divided by the mirror 301.According to such a construction, it is necessary to control the outputof the laser diode 32 via the control unit 162 in response to the outputof the photodetector 142. By doing so, it becomes possible to constructan optical module of simple construction and reduced number of parts.

[0830] [Twenty-Fifth Embodiment]

[0831] Next, another embodiment of the present invention will bedescribed.

[0832] Conventionally, edge-emission laser diodes are used extensivelyin optical telecommunication systems. When using such an edge emissionlaser diode in combination with plural optical fibers, there is a needof achieving optical coupling for each of the laser diodes one by one.In the case of an edge-emission laser diode, there is another problem oflarge beam divergence in that the laser beam spreads rapidly due to thelarge emission angle. Further, the emission angle is different in thelateral direction and vertical direction, and the laser bean shows anelongated beam spot characterized by poor aspect ratio. Thus, in thecase of conventional edge-emission laser diode, it has been necessary toprovide a coupling lens for each of the laser diodes.

[0833] Because of these reasons, it was not possible to form the laserdiode in the form of high density array in the case of usingconventional edge-emission type laser diode.

[0834] In contrast, the present invention has enabled the constructionof a high-density laser array by using a number of surface-emissionlaser diodes commonly on a single chip monolithically. By combiningoptical fibers with the laser diode array thus formed, a large capacityoptical transmission system is realized.

[0835]FIGS. 110A and 110B show an example of an opticaltelecommunication system in which the long-wavelength laser diodes of1.1-1.7 μm are used in combination with optical fibers.

[0836] As represented in FIG. 110A, the surface-emission laser diode ofthe present invention is characterized by a narrow divergence of theoptical beam in any of the horizontal and lateral directions of the beamspot. In fact, the laser beam produced by such a surface-emission laserdiode is characterized by a circular beam cross-section.

[0837] In contrast, the laser diode of the edge emission type laserdiode produces an optical beam diverging rapidly with large emissionangle, wherein the laser beam produced by such an edge-emission layerdiode shows a beam shape characterized by an eclipse. Thus, the size ofthe laser beam spot is different in the horizontal direction verticaldirection.

[0838] Thus, by using the surface-emission laser diode of the presentinvention, it becomes possible to construct a large capacity opticaltransmission system by arranging a number of optical fibers with highdensity.

[0839] In the case of such a high-density telecommunication system, itis difficult to use coloring layer or identification ring used commonlyin ordinary optical fiber capes for identifying reach of the opticalfibers In the cable.

[0840] In the case of the surface-emission laser diode, it is possibleto form each beam emission part 32A constituting the arraysimultaneously and in high density by using the lithographic process. Inthe case of handling a number of optical fibers in such a laser diodearray, it is more preferable to handle the optical fibers in the form ofbundle, rather than handing each of the optical fibers. Particularly, itis preferable to make a correlation between the optical fibers bundledin the form of a cable and the laser diodes in the array.

[0841] On the other hand, in the case the optical fibers 101 areassembled to form a bundle, it is not easy to identify the center of thebundle or individual optical fibers in the bundle.

[0842] For example, in the case the cladding 101 b of the optical fiber101X at the center of the optical fiber bundle is colored as representedin FIGS. 11A-11C, the recognition of the optical fiber is easy.

[0843] Thus, it is possible to achieve the correlation between the laserdiodes in the array and the optical fibers in the bundle by firstturning on the laser diode 32AZ at the center of the array. Thereby thislaser diode is correlated with the colored optical fiber at the centerof the bundle.

[0844] In the example of FIGS. 112, it can be seen that four fibers arecolored at cladding layer. By correlating these four optical fibers withfour laser diodes, it is possible to easily establish the correspondencebetween the optical fiber and the laser diode for other optical fibers.

[0845] It should be noted that the cladding layer of an optical fiber isused merely for confining the light in the core. Thus, coloring of thecladding layer 101 b as shown in FIGS. 113A and 113B does not cause aproblem at all with regard to the information transmission, which takesplace through the core 110 a.

[0846]FIGS. 111B and 111C show a modification of FIG. 111A. In theexample of FIG. 111A, the optical fibers 101 are arranged in a closestpacking state. In the case of FIG. 111B, on the other hand, opticalfibers are arranged in a square grid. Further, FIG. 111C shows anexample of uses a ferule 101F for marinating the square grid arrangementof the optical fibers.

[0847]FIG. 114 shows an example of a single mode optical fiber. Ascompared with the optical fibers of multimode represented in FIGS. 113Aand 113C, the core diameter of the single mode optical fiber is verysmall with regard to the diameter of the cladding layer of 125 μm, andthe area of the cladding layer 101 b with respect to the core 101 a canreach 172 times as large as the core area of the multimode optical fiberIn the case of the single mode fiber, recognition of the optical fiberby using the color layer is facilitated further.

[0848] [Twenty-Sixth Embodiment]

[0849] Next, another embodiment of the present is invention will beexplained. In the conventional laser diode, there has been a problemthat the threshold current is changed depending on the temperature. In atelecommunication system, the use of the laser diode at strictlyconstant temperature is difficult. Thus, in the case of theedge-emission laser diode, it has been practiced to detect the leakagelight emitted in the backward direction by a photodetector and theoutput off the photodetector has been used for a feed back control ofthe laser outputs such that the output of the laser diode is maintainedconstant.

[0850] In the case of the surface-emission laser diode, however, suchdetection of the leakage light is not possible. Thus, in theconventional surface-emission laser diode, it has been practiced toprovide a photodetector between the laser diode and the optical fiber orat the downstream side of the optical fiber, and the feed back controlhas been applied by using such a photodetector such that the output ofthe laser diode is maintained constant.

[0851]FIG. 115 shows an example of the I-L (current-optical output)characteristic of the long-wavelength laser diode of the presentinvention.

[0852] Referring to FIG. 115, the laser diode of the present inventionhas a feature, contrary to the conventional laser diode, in that thechange of the threshold current with temperature is very small. Only theslope of the curve is influenced with the temperature.

[0853] Thus, as long as the laser diode is driven at a constant drivevoltage, the change of the optical output is small even in the casethere is a temperature change.

[0854] For example, in the case the laser diode is driven at the drivecurrent of 6 mA in FIG. 115, the change of optical output associatedwith the temperature change from 10° C. to 70° C. is only 0.1 mW. Evenwhen the temperature is changed from 10° C. to 100° C., the change ofthe optical output is only 0.25 mW. In terms of S/N ratio, this isrespectively 26 dB and 18 dB. Thus, the laser diode of the presentinvention can provide a sufficient signal quality in the commonly usedtemperature environment of 20-70° C.

[0855] It should be noted that the drift of current of a constantcurrent source is in the order of ±2-3% Thus, it is easy to achieve aconstant current control.

[0856] Thus, by setting the upper limit and lower limit for the opticaloutput and further setting the upper limit and lower limit for thetemperature, the present embodiment achieves the desires control of theoptical output within the foregoing upper and lower limits bycontrolling the drive current at a constant value x between a firstreference drive current a corresponding to the upper limit opticaloutput at the lower limit temperature and a second reference drivecurrent b corresponding to the lower limit optical output at the upperlimit temperature.

[0857] According to the present invention, the laser diode is driven ata constant current determined with respect to the target optical output.

[0858] [Twenty-Seventh Embodiment]

[0859] The threshold current of the laser diode increases gradually withtime and when the threshold current has exceeded a predetermined value,it is the lifetime of the laser diode.

[0860] Thus, there is a demand to avoid deterioration of signal qualityeven when the aging is in progress.

[0861] As shown in FIG. 117, for example, there is provided a halfmirror 411 in the transmission path 410 coupled to the laser diode 32,and the optical beam thus divided is detected by the photodetectiondevice 412. In this case, the intensity of the laser beam detected bythe photodetection device, in other words the monitor optical strength,is fed back to the control unit 415 and the constant current source 416.

[0862] In the illustrated example, the output of the photodetecciondevice 412 is supplied to the communication control unit 414, and thecommunication control unit 414 obtains the correction of the drivecurrent by referring to a conversion table 414A representing therelationship between the monitor optical output and the correction ofthe drive current. According to such a construction, it is possible toeliminate the effect of aging by removing s the change of optical outputcaused by aging. Thereby, a practical telecommunication system isrealized.

[0863] In order to monitor for the aging or anomaly related to theaging, it is sufficient that the output of the photodetection device atthe reception end can be obtained. Thus, it is also possible to transmitthe reading of the photodetection device at the reception side in theform of data to the transmission side. For example, it is possible totransmit the reading of the photodetection device periodically or at anytime to the optical transmission side, separately to the opticaltelecommunication data. The data thus transmitted may be forwarded inthe transmission side from the communication control unit to the lasercontrol unit for correcting the drive current. By doing so, it ispossible to eliminate the fluctuation of optical output caused by aging.

[0864] [Twenty-Eighth Embodiment]

[0865] Next, a further embodiment of the present invention will bedescribed.

[0866]FIG. 118 shows an example of an optical telecommunication systemthat uses a long-wavelength laser diode 32 of the present invention.

[0867] Referring to FIG. 118, it can be seen that the system includes alaser diode module connected with an optical fiber 421, an opticalcircuit substrate 423 carrying the laser diode module 422, andelectronic substrates 423B and 423C provided above and below the opticalcircuit substrate 423A. The circuit substrates 423A-423C areaccommodated in a case 420, wherein the substrates 423A-423C form a airflow path in the case 420. Further, the case 420 is provided with a fan424A, and an air outlet is formed on the case 420 at the side oppositeto the fan 424A. The electronic substrates 423B and 423C carryelectronic components 423 a thereon.

[0868] The fan 424A may be a compulsory air-feeding fan such as siroccofan, and supplies a cooling air inside the case 420. The cooling airflows along the space between the substrates 423B and 423C and theretakes place heat exchange between the air and the laser diode module 422as the cooling air is caused flow along the substrates. The cooling airthus exchanged heat is expelled from the air outlet.

[0869]424B

[0870] In the illustrated example, the substrate 423B of the smallestheat generation is provided at the lower part and the substrate 423Ccausing a larger heating is provided thereabove.

[0871] It should be noted that the surface of the optical substrate 423Afacing the electronic substrate 423C is reduced with projections ordepressions so as to minimize disturbance of air flow. Meanwhile, asimilar effect is obtained also in the case in which a flat boardcarrying no electronic components is used for the electronic substrates423B or 423C While the present embodiment uses only one fan 424A, it ispossible to increase the number of fans with the number of the laserdiodes provided in the case 420. It should be noted that the heating isincreased when the number of the laser diodes is increased.Alternatively, it is possible to increase the flow rate of the air. Inthis case, the area of the air outlet has to be increased.

[0872] It is also possible to use the fan 424A to pull the air insidethe case 420. Further, it is possible to provide a fan in the air intakeside and another fan in the air outlet side.

[0873] [Twenty-Ninth Embodiment]

[0874]FIG. 119 shows an example of the laser diode module that uses thelong-wavelength laser diode 32 of the present invention.

[0875] Referring to FIG. 119, it can be seen that two laser diodes 32Aare formed on the GaAs substrate 32 monolithically, and the GaAssubstrate 32 is carried by a Si mount substrate 131 having a largethermal conductivity. Further, the Si substrate 131 is carried on aceramic substrate 1363 having a still larger thermal conductivity. Theceramic substrate 136 is mounted on an optical circuit board such as thesubstrate 434A shown in FIG. 101. The ceramic substrate 136 is cooled.

[0876] Further, electric interconnection to the laser diode 32A isprovided by way of bonding wires connecting an electrode 136A on theceramic substrate 136 and the electrode on the laser diode 32A.

[0877] With such a construction, the heat generated by the laser diode32A is transferred to the GaAs substrate by thermal conduction and thento the Si substrate 131 of lower temperature. Further, the heat istransferred to the ceramic substrate 136 of lower temperature, andefficient cooling of the laser diode 32A becomes possible. It should benoted that the surface area of the ceramic substrate 136 is the largestamong the constituent parts, and thus, the ceramic substrate 136 iscooled efficiently by radiation and contact with the air.

[0878] The GaAs substrate constituting the laser diode chip of thepresent invention has a thermal conductivity of 0.54W/cmK, while it isnoted that the thermal conductivity of Si is 1.48W/cmK. Further, amaterial having a larger thermal conductivity than Si such as BeO(2.72W/cmK) or diamond (9.0W/cmK) can also be used, wherein the value ofthe thermal conductivity is the value at 300K.

[0879] Meanwhile, thermal transfer across tow substrates contacting witheach other can be increased by reducing the surface roughness andincreasing the intimateness. On the other hand, excessive processing ofthe surface merely invites increase of cost and the improvement of heattransfer is little. For example, the precision of surface flatnessbeyond 10 nm merely increases the cost and is not practical Thus, thelower limit of the surface roughness should be around 10 nm.

[0880] With regard to the upper limit of surface roughness, excessivelyrough surface is disadvantageous for contacting two substrates. Thus,the inventor of the present invention conducted extensive study aboutthis matter and discovered that the surface roughness of 1000 nm or lessis sufficient for guaranteeing intimate contact and excellent heattransfer. In the experiments conducted by causing the laser diode tooscillate, it was confirmed that the heat generated by the laser diode32A is transferred from the laser diode chip 32 to the first substrate131, and to the second substrate 136, without causing accumulation ofheat. With this, it became possible to reduce the fluctuation ofthreshold current of the laser diode caused by heating. Thereby, itbecame possible to cause the laser diode to oscillate stably.

[0881]FIG. 120 show an example of the long-wavelength laser diode moduleof the present embodiment, wherein the GaAs substrate 32 carrying thelaser diode 32A is fixed upon the Si mount substrate 131 via a thermalconduction layer 137, and the Si mount substrate 131 is mounted on theceramic substrate 136 via another thermal conduction layer 138.

[0882] In the present embodiment, the contact surfaces of the substrates32, 131 and 136 are polished by using an alumina abrasive to a surfaceroughness Ra of 10-1000 nm, and any gap formed therebetween is filledwith the thermal conductive layer 137 or 138.

[0883] Here, it should be noted that the thermal conductive layer 137 or138 may be formed of an organic polymer material such as epoxy resin orsilicone resin or acryl resin dispersed with metal powders such asaluminum or gold or silver or copper.

[0884] The metal powders have a diameter of several nanometers to 100 nmand the resin layer is applied with a thickness of 3-100 μm. Theproportion of the metal powders was set to 0.1-1 part with regard to 1part of resin.

[0885]FIG. 121 is an example of a long-wavelength laser diode of thepresent embodiment and is formed of a laser module package 431 includingthe laser diode module 422 of FIG. 118 and an optical fiber 421.

[0886] At the bottom part of the package 431, there is provided acooling fin structure 431A having eight cooling fins each having arectangular cross-section, with a base length of 1 mm and a height of 3mm, and the cooling air is caused to flow along the cooling finstructure 431A.

[0887] It should be noted that the outer surface of the laser modulepackage 431 performs also as a heat-radiating member similar to theceramic substrate 136, in addition to the function of the packaging ofthe laser diode. It should be noted that the surface on which thecooling fins are provided ins not limited to the bottom surface but maybe other surface along with the cooling air is caused to flow. Further,the number and construction of the cooling fins are by no means limitedto the one illustrated.

[0888] The point of the present embodiment is to provide, in a heatradiating structure in which a first substrate including a heat sourceand a second substrate not including a heat source are stacked, suchthat the surface area of the part of the second substrate not contactingwith the first substrate is set larger than the surface area of thesecond substrate contacting with the first substrate. Any of thestructure may be used in place of the cooing fin as long the structureincreases the surface area of the second substrate.

[0889] As noted previously, in the surface-emission laser diodeoscillating at the wavelength of 1.1-1.7 μm, it is possible to form anumber of laser diodes on a common chip and is suitable for largecapacity optical telecommunication system. However, design of such aconstruction including a large number of laser diode has to be madecarefully in view of severe heating. The present embodiment provides asolution to this problem. Larger the number of the laser diodes, moreeffective the construction of the present embodiment.

[0890] [Thirtieth Embodiment]

[0891]FIGS. 122 and 123 show another embodiment of the presentinvention, wherein FIGS. 122 shows the case a number of long-wavelengthsurface-emission laser diodes 32A of the present invention are used toform a one-dimensional array, while FIG. 133 show the case the laserdiodes form a two-dimensional array.

[0892] In the drawings, the laser diode elements 32A provided withshading have corresponding photodetection devices, while other elementshave no photodetection device and the output thereof is taken to theoutside.

[0893]FIG. 124 shows the construction of FIG. 122 from a different angleIt can be seen that the laser diode elements 32A provided with theshading is provided with the photodetection device 142P and thephotodetection device 142P interrupts the laser beam. On the other hand,the laser beam of the laser diode 32A not provided with thephotodetection device 142P is injected into the optical fiber 352 by thelens 353.

[0894] The optical output of the laser diode 32A not provided with thephotodetector 142P is calculated based on the output of thephotodetector(s) 142P located in the vicinity thereof. Based on theoutput of the photodetector 142P thus 110 obtained, output of each ofthe laser diodes 32A is controlled. The variation of output between thelaser diodes 32A is easily corrected by using a correction coefficientobtained in advance FIGS. 125-127 show an example of output control ofthe laser diode using the construction of FIG. 124.

[0895] Referring to FIG. 125, the laser diode chip 32 includes aone-dimensional array of laser diodes 32A similar to FIG. 122. For thesake of convenience of explanation, the laser diodes 32A in FIG. 125 areprovided with numbers (0)-(6).

EXAMPLE 1

[0896] In Example 1, the out put of the photodetection device 142P thatmonitors the output of the first laser diode 32A (1) is used forcontrolling the drive currents of the laser diodes 32A (0)-(6) of FIG.125 by using the driver circuit 106 of FIG. 106 such that

[0897] I₀ is controlled based on the value of a₀O₀;

[0898] I₁ is controlled based on the value of a₁O₀;

[0899] I₂ is controlled based on the value of a₂O₀;

[0900] I₃ is controlled based on the value of a₃O₀;

[0901] I₄ is controlled based on the value of a₄O₀;

[0902] I₅ is controlled based on the value of a₅O₀; and

[0903] I₆ is controlled based on the value of a₆O₀,

[0904] wherein Ii represents the drive current of the i-th (i=0−6) laserdiode 32A and O1 represents the optical output of the i-th laser diode32A. Further, a_(i) represents a correction coefficient and isdetermined in advance by measuring the output of respective laser diodessuch that the output calculated based on the drive current is closest tothe actual laser output.

EXAMPLE 2

[0905] In Example 2, the out put of the photodetection device 142P thatmonitors the output of the first laser diode 32A (1) is used forcontrolling the drive currents of the laser diodes 32A (0)-(6) of FIG.125 by using the driver circuit 106 of FIG. 106 such that

[0906] I₀ is controlled based on the value of a0O0;

[0907] I₁ is controlled based on the value of a₁O₀+b₁O₃;

[0908] I₂ is controlled based on the value of a₂O₀+b₂O₃;

[0909] I₃ is controlled based on the value of a₃O₃;

[0910] I₄ is controlled based on the value of a₄O₀+b₄O₆;

[0911] I₅ is controlled based on the value of a₅O₀+b₅O₆; and

[0912] I₆ is controlled based on the value of a₆O₆.

EXAMPLE 3

[0913] In Example 3, the out put of the photodetection device 142P thatmonitors the output of the first laser diode 32A (1) is used forcontrolling the drive currents of the laser diodes 32A (00)-(44) of FIG.128 by using the driver circuit 106 of FIG. 106 such that

[0914] I₀₀ is controlled based on the value of a₀₀O₀₀;

[0915] I₀₁ is controlled based on the value of a₀₁O₀₀;

[0916] I₁₀ is controlled based on the value of a₁₀O₀₀;

[0917] I₁₁ is controlled based on the value of a₁₁O₀₀;

[0918] I₀₂ is controlled based on the value of a₀₂O₀₃;

[0919] I₀₃ is controlled based on the value of a₀₃O₀₃;

[0920] I₀₄ is controlled based on the value of a₀₄O₀₃,

[0921] I₁₂ is controlled based on the value of a₁₂O₀₃;

[0922] I₁₃ is controlled based on the value of a₁₃O₀₃;

[0923] I₁₄ is controlled based on the value of a₁₄O₀₃,

[0924] wherein a_(ij) is a correction coefficient.

EXAMPLE 4

[0925] In the example of FIG. 129, the ij-th laser diode 32A of FIG. 129is controlled such that

[0926] I₀₀ is controlled based on the value of a₀₀O₀₀;

[0927] I₀₁ is controlled based on the value of a₀₁O₀₀+b₀₁O₀₄+c₀₁O₂₂;

[0928] I₁₁ is controlled based on the value of a₁₁O₀₀+b₁₁O₂₂;

[0929] I₂₁ is controlled based on the value of a₂₁O₀₀+b₂₁O₂₂+c₂₁O₁₀;

[0930] In Example, 4, a_(ij), b_(ij) and c_(ij) are correctioncoefficients.

[0931] [Thirty-First Embodiment]

[0932] Next a further embodiment of the present invention will beexplained.

[0933] The present embodiment is related to the production control ofthe laser array module that uses the laser diode of the presentinvention and used for the long-wavelength optical telecommunication.

[0934] Here, it should be noted that the laser array module means that aplurality of surface-emission laser diodes are provided in the form of amodule and includes the case in which a number of laser diodes areformed on a single chip or the case in which a number of such chips arearranged. Further, the case of plural chips, each carrying a singlelaser diode, are arranged is also included.

[0935] In the production process of such a laser diode module, laserchip modules carrying a laser diode array are produced.

[0936] In such a production process, a predetermined number of laserdiode devices or laser diode chips are prepared and these elements arearranged to form the desired laser array module.

[0937] Thereafter, an inspection process is conducted with regard to thelaser diode modules, wherein the inspection is conducted for each of thelaser diode chips and each of the laser diodes. Upon confirmation that adesired quality is achieved for each of the devices and each of thechips, the laser array module becomes the state ready for shipping.

[0938] In the case there is detected a single device out of n devices oflaser diode chips arranged to form the laser array module is defective,the laser chip module is treated as a defective product.

[0939] On the other hand, if it is possible to treat a laser chipmodule, in which the number c of the defective laser diodes or chips iswithin a predetermined number n of good products, as being a goodproduct, the productivity of the laser array module is increasedsignificantly.

[0940] The inventor of the present invention realized the importance ofsuch a product control process and diligently studied the productioncontrol process applicable to the case of producing a product that usesa large number of elements each performing, a single and same functionas other elements.

[0941] Hereinafter, the present embodiment will be described withreference to FIGS. 130 and 131.

[0942] Referring to FIG. 130, the production of the laser diode or chipis conducted according to the step S1 of wafer process step, step S2 forproducing a laser diode array step, and S3 for producing a laser arraymodule. Further, there is provided an inspection step S4 for inspectingthe array or module produced by the steps S2 and S3.

[0943] In the present embodiment, the laser array module that turned outto include a defective device or defective chip is not immediatelytreated as a defective product. In the event the number c of the defectsis within a certain threshold (n-c) (n is the total number of thedevices or chips in the module), the product is shipped as the producthaving the quality of (n-c) In the process of FIG. 113, this examinationstep is conducted at the step S6. In the case the entire chips n aredefective, the laser diode module is treated as a defective device.

[0944] Thus, in the step S4, of FIG. 131, an inspection step 541 isconducted for evaluating the product quality for each channel CH byusing a high-frequency probe or analyzer.

[0945] The data of the product quality for each channel thus obtained isthen examined in the product examination step S42, wherein the step S42judges whether or not the required quality is satisfied for all of thelaser diodes or chips. The judgment is made with regard to the itemssuch as I-L characteristic, I-V characteristic, fiber coupling loss,pulse modulation characteristic, temperature dependence, and the like.Thereby, the laser array modules are shipped according to the gradescorresponding to the number of the properly functioning laser diodechips.

[0946] From the explanation noted above, it will be apparent that thepresent embodiment enables the use of most of the laser array modules,used for the optical telecommunication system by using thesurface-emission laser diode of 1.1-1.7 μm, according to the conditionof the module.

[0947] According to the present embodiment, therefore, the laser arraymodules are used effectively even in the case only n-c of the laserdiodes operate properly, and the loss of the laser array module duringthe production process is minimized.

[0948] The present invention is not limited to the embodiments describedheretofore, but various variations and modifications may be made withoutdeparting from the scope of the invention.

[0949] The present application is based on Japanese priorityapplications No.2001-050145 filed on Feb. 26, 2001, No. 2001-050171filed on Feb. 26, 2001, No.2001-050083 filed on Feb. 26, 2001,No.2001-051253 filed on Feb. 26, 2001, No.2001-051256 filed on Feb. 26,2001, No.2001-051266 filed on Feb. 26, 2001, No.2001-053213 filed onFeb. 27, 2001, No.2001-053218 filed on Feb. 27, 2001, No.2001-053200filed on Feb. 27, 2001, No.2001-053200 filed on Feb. 27, 2001,No.2001-053190 filed on Feb. 27, 2001, No.2001-053225 filed on Feb. 27,2001, No.2001-073767 filed on Mar. 15, 2001, No.2001-090711 filed onMar. 27, 2001, No.2002-019748 filed on Jan. 29, 2002, No.2002-033590filed on Feb. 12, 2002, the contents of which are hereby incorporated byreference.

What is claimed is:
 1. A distributed Bragg reflector, comprising: afirst semiconductor layer having a first, larger refractive index; asecond semiconductor layer having a second, lower refractive index, saidfirst and second semiconductor layers being stacked alternately, amaterial layer having a refractive index intermediate between said firstand second refractive indices, said distributed Bragg reflector beingtuned to a wavelength of 1.1 μm or longer, wherein there is provided amaterial layer having a refractive index intermediate between said firstrefractive index and said second refractive index, said material layerhaving a thickness equal to or larger than 5 nm but equal to or smallerthan 50 nm.
 2. A distributed Bragg reflector as claimed in claim 1,wherein said material layer has a thickness equal to or larger than 20nm.
 3. A distributed Bragg reflector as claimed in claim 1, wherein saidmaterial layer has a thickness equal to or larger than 30 nm.
 4. Adistributed Bragg reflector as claimed in claim 2, wherein said firstand second semiconductor layers are formed of any of AlAs, GaAs andAlGaAs, and wherein there is a difference of Al content of less than 80%between said first semiconductor layer and said second semiconductorlayer.
 5. A distributed Bragg reflector as claimed in claim 3, whereinsaid first semiconductor layer and said second semiconductor layer areformed of any of AlAs, GaAs and AlGaAs, and wherein there is adifference of Al content of 80% or more between said first semiconductorlayer and said second semiconductor layer.
 6. A distributed Braggreflector, comprising: a first semiconductor layer having a first,larger refractive index; a second semiconductor layer having a second,lower refractive index, said first and second semiconductor layers beingstacked alternately, a material layer having a refractive indexintermediate between said first and second refractive indices, saiddistributed Bragg reflector being tuned to a wavelength of 1.1 μm orlonger, wherein there is provided a material layer having a refractiveindex intermediate between said first refractive index and said secondrefractive index, said material layer having a thickness smaller than(50λ−15) [nm] where λ is a tuned wavelength of the distributed Braggreflector.
 7. A distributed Bragg reflector as claimed in claim 6,wherein said material layer has a thickness of 20 nm or more.
 8. Adistributed Bragg reflector as claimed in claim 6, wherein said materiallayer has a thickness of 30 nm or more.
 9. A distributed Braggreflector, comprising: a first semiconductor layer having a first,smaller bandgap; a second semiconductor layer having a second, largerbandgap, said first and second semiconductor layers being stackedalternately, a material layer having a bandgap intermediate between saidfirst and second bandgaps, provided between said first and secondsemiconductor layer, said material layer changing a valence band energythereof in a thickness direction from said first semiconductor layer tosaid second semiconductor layer, said material layer comprising a firstlayer adjacent to said first semiconductor layer and a second layeradjacent to said second semiconductor layer, said first layer and secondlayer having first and second rates of compositional change such thatsaid first rate being larger than said second rate.
 10. A distributedBragg reflector as claimed in claim 9, wherein said intermediate layerchanges said valence band energy continuously and gradually from saidfirst semiconductor layer to said second semiconductor layer.
 11. Adistributed Bragg reflector as claimed in claim 9, wherein saidintermediate layer changes said valence band energy stepwise from saidfirst semiconductor layer to said second semiconductor layer.
 12. Adistributed Bragg reflector as claimed in claim 9, wherein saidintermediate layer comprises a layer in which said valence band energychanges continuously and a layer in which said valence band energychanges stepwise.
 13. A distributed Bragg reflector as claimed in claim9, wherein said first and second layers have respective first and secondthicknesses, such that said first thickness is smaller than said secondthickness.
 14. A distributed Bragg reflector as claimed in claim 9,wherein there is a stepped change of valence band energy at an interfacebetween said first semiconductor layer and said material layer.
 15. Adistributed Bragg reflector as claimed in claim 9, wherein said firstand second semiconductor layers comprise a material of AlGaAs system.16. A distributed Bragg reflector as claimed in claim 9, wherein saidfirst and second semiconductor layers comprise a material of AlGaAsPsystem.
 17. A distributed Bragg reflector as claimed in claim 9, whereinsaid first and second semiconductor layers and said intermediate layerhave a carrier density of 5×10¹⁷ cm⁻³-2×10¹⁸ cm⁻³, and wherein saidintermediate layer has a thickness in the rage of 5-40 nm, and whereinsaid intermediate layer is characterized by an average change rate of Alcontent in the range of 0.02-0.05 nm.
 18. A surface-emission laserdiode, comprising: an active layer; and a resonator cooperating withsaid active layer, said active layer comprising upper and lowerreflectors disposed above and below said active layer, at least one ofsaid upper and lower reflectors comprising a distributed Braggreflector, comprising: a first semiconductor layer having a first,larger refractive index; a second semiconductor layer having a second,lower refractive index, said first and second semiconductor layers beingstacked alternately, a material layer having a refractive indexintermediate between said first and second refractive indices, saiddistributed Bragg reflector being tuned to a wavelength of 1.1 μm orlonger, wherein there is provided a material layer having a refractiveindex intermediate between said first refractive index and said secondrefractive index, said material layer having a thickness equal to orlarger than 5 nm but equal to or smaller than 50 nm.
 19. Asurface-emission laser diode as claimed in claim 18, wherein saidmaterial layer has a thickness equal to or larger than 20 nm.
 20. Asurface-emission laser diode as claimed in claim 18, wherein saidmaterial layer has a thickness equal to or larger than 30 nm.
 21. Asurface-emission laser diode as claimed in claim 19, wherein said firstand second semiconductor layers are formed of any of AlAs, GaAs andAlGaAs, and wherein there is a difference of Al content of less than 80%between said first semiconductor layer and said second semiconductorlayer.
 22. A surface-emission laser diode as claimed in claim 20,wherein said first semiconductor layer and said second semiconductorlayer are formed of any of AlAs, GaAs and AlGaAs, and wherein there is adifference of Al content of 80% or more between said first semiconductorlayer and said second semiconductor layer.
 23. A surface-emission laserdiode as claimed in claim 18, wherein said active layer is formed of anyof a GaNAs layer, a GaInAs layer, a GaInNAs layer, a GaAsSb layer, aGaInAsSb layer, and a GaInNAsSb layer.
 24. A surface-emission laserdiode, comprising: an active layer; and a resonator cooperating withsaid active layer, said active layer comprising upper and lowerreflectors disposed above and below said active layer, at least one ofsaid upper and lower reflectors comprising a distributed Braggreflector, comprising: a first semiconductor layer having a first,larger refractive index; a second semiconductor layer having a second,lower refractive index, said first and second semiconductor layers beingstacked alternately, a material layer having a refractive indexintermediate between said first and second refractive indices, saiddistributed Bragg reflector being tuned to a wavelength of 1.1 μm orlonger, wherein there is provided a material layer having a refractiveindex intermediate between said first refractive index and said secondrefractive index, said material layer having a thickness smaller than(50λ−15) [nm] where λ is a tuned wavelength of the distributed Braggreflector.
 25. A surface-emission laser diode as claimed in claim 24,wherein said material layer has a thickness of 20 nm or more.
 26. Asurface-emission laser diode as claimed in claim 24, wherein saidmaterial layer has a thickness of 30 nm or more.
 27. A surface-emissionlaser diode as claimed in claim 24, wherein said active layer is formedof any of a GaNAs layer, a GaInAs layer, a GaInNAs layer, a GaAsSblayer, a GaInAsSb layer, and a GaInNAsSb layer.
 28. A surface-emissionlaser diode, comprising: an active layer; and a resonator cooperatingwith said active layer, said active layer comprising upper and lowerreflectors disposed above and below said active layer, at least one ofsaid upper and lower reflectors comprising a distributed Braggreflector, comprising: a first semiconductor layer having a first,smaller bandgap; a second semiconductor layer having a second, largerbandgap, said first and second semiconductor layers being stackedalternately, a material layer having a bandgap intermediate between saidfirst and second bandgaps, provided between said first and secondsemiconductor layer, said material layer changing a valence band energythereof in a thickness direction from said first semiconductor layer tosaid second semiconductor layer, said material layer comprising a firstlayer adjacent to said first semiconductor layer and a second layeradjacent to said second semiconductor layer, said first layer and secondlayer having first and second rates of compositional change such thatsaid first rate being larger than said second rate.
 29. Asurface-emission laser diode as claimed in claim 28, wherein saidintermediate layer changes said valence band energy continuously andgradually from said first semiconductor layer to said secondsemiconductor layer.
 30. A surface-emission laser diode as claimed inclaim 28, wherein said intermediate layer changes said valence bandenergy stepwise from said first semiconductor layer to said secondsemiconductor layer.
 31. A surface-emission laser diode as claimed inclaim 28, wherein said intermediate layer comprises a layer in whichsaid valence band energy changes continuously and a layer in which saidvalence band energy changes stepwise.
 32. A surface-emission laser diodeas claimed in claim 28, wherein said first and second layers haverespective first and second thicknesses, such that said first thicknessis smaller than said second thickness.
 33. A surface-emission laserdiode as claimed in claim 28, wherein there is a stepped change ofvalence band energy at an interface between said first semiconductorlayer and said material layer.
 34. A surface-emission laser diode asclaimed in claim 28, wherein said first and second semiconductor layerscomprise a material of AlGaAs system.
 35. A surface-emission laser diodeas claimed in claim 28, wherein said first and second semiconductorlayers comprise a material of AlGaAsP system.
 36. A surface-emissionlaser diode as claimed in claim 28, wherein said first and secondsemiconductor layers and s aid intermediate layer have a carrier densityof 5×10¹⁷ cm⁻³-2×10¹⁸ cm⁻³, and wherein said intermediate layer has athickness in the rage of 5-40 nm, and wherein said intermediate layer ischaracterized by an average change rate of Al content in the range of0.02-0.05 nm⁻¹.
 37. A laser diode array, comprising: a substrate; and aplurality of surface-emission laser diodes formed commonly on saidsubstrate, each of said plurality of surface-emission laser diodescomprising: an active layer; and a resonator cooperating with saidactive layer, said active layer comprising upper and lower reflectorsdisposed above and below said active layer, at least one of said upperand lower reflectors comprising a distributed Bragg reflector,comprising: a first semiconductor layer having a first, largerrefractive index; a second semiconductor layer having a second, lowerrefractive index, said first and second semiconductor layers beingstacked alternately, a material layer having a refractive indexintermediate between said first and second refractive indices, saiddistributed Bragg reflector being tuned to a wavelength of 1.1 μm orlonger, wherein there is provided a material layer having a refractiveindex intermediate between said first refractive index and said secondrefractive index, said material layer having a thickness equal to orlarger than 5 nm but equal to or smaller than 50 nm.
 38. A laser diodearray, comprising: a substrate; and a plurality of surface-emissionlaser diodes formed commonly on said substrate, each of said surfaceemission laser diodes comprising: an active layer; and a resonatorcooperating with said active layer, said active layer comprising upperand lower reflectors disposed above and below said active layer, atleast one of said upper and lower reflectors comprising a distributedBragg reflector, comprising: a first semiconductor layer having a first,larger refractive index; a second semiconductor layer having a second,lower refractive index, said first and second semiconductor layers beingstacked alternately, a material layer having a refractive indexintermediate between said first and second refractive indices, saiddistributed Bragg reflector being tuned to a wavelength of 1.1 μm orlonger, wherein there is provided a material layer having a refractiveindex intermediate between said first refractive index and said secondrefractive index, said material layer having a thickness smaller than(50λ−15) [nm] where λ is a tuned wavelength of the distributed Braggreflector.
 39. A surface-emission laser diode array, comprising: asubstrate; and a plurality of laser diodes, each of saidsurface-emission laser diodes, comprising: an active layer; and aresonator cooperating with said active layer, said active layercomprising upper and lower reflectors disposed above and below saidactive layer, at least one of said upper and lower reflectors comprisinga distributed Bragg reflector, comprising: a first semiconductor layerhaving a first, smaller bandgap; a second semiconductor layer having asecond, larger bandgap, said first and second semiconductor layers beingstacked alternately, a material layer having a bandgap intermediatebetween said first and second bandgaps, provided between said first andsecond semiconductor layer, said material layer changing a valence bandenergy thereof in a thickness direction from said first semiconductorlayer to said second semiconductor layer, said material layer comprisinga first layer adjacent to said first semiconductor layer and a secondlayer adjacent to said second semiconductor layer, said first layer andsecond layer having first and second rates of compositional change suchthat said first rate being larger than said second rate.
 40. An opticalinterconnection system, comprising: a surface-emission laser diode; andan optical transmission path coupled optically to said surface-emissionlaser diode, said surface-emission laser diode comprising: an activelayer; and a resonator cooperating with said active layer, said activelayer comprising upper and lower reflectors disposed above and belowsaid active layer, at least one of said upper and lower reflectorscomprising a distributed Bragg reflector, comprising: a firstsemiconductor layer having a first, larger refractive index; a secondsemiconductor layer having a second, lower refractive index, said firstand second semiconductor layers being stacked alternately, a materiallayer having a refractive index intermediate between said first andsecond refractive indices, said distributed Bragg reflector being tunedto a wavelength of 1.1 μm or longer, wherein there is provided amaterial layer having a refractive index intermediate between said firstrefractive index and said second refractive index, said material layerhaving a thickness equal to or larger than 5 nm but equal to or smallerthan 50 nm.
 41. An optical interconnection system, comprising: asurface-emission laser diode; and an optical transmission path coupledoptically to said surface-emission laser diode, said surface-emissionlaser diode comprising: an active layer; and a resonator cooperatingwith said active layer, said active layer comprising upper and lowerreflectors disposed above and below said active layer, at least one ofsaid upper and lower reflectors comprising a distributed Braggreflector, comprising: a first semiconductor layer having a first,larger refractive index; a second semiconductor layer having a second,lower refractive index, said first and second semiconductor layers beingstacked alternately, a material layer having a refractive indexintermediate between said first and second refractive indices, saiddistributed Bragg reflector being tuned to a wavelength of 1.1 μm orlonger, wherein there is provided a material layer having a refractiveindex intermediate between said first refractive index and said secondrefractive index, said material layer having a thickness smaller than(50λ−15) [nm] where λ is a tuned wavelength of the distributed Braggreflector.
 42. An optical interconnection system, comprising: asurface-emission laser diode; and an optical transmission path coupledoptically to said surface-emission laser diode, said surface-emissionlaser diode comprising: an active layer; and a resonator cooperatingwith said active layer, said active layer comprising upper and lowerreflectors disposed above and below said active layer, at least one ofsaid upper and lower reflectors comprising a distributed Braggreflector, comprising: a first semiconductor layer having a first,smaller bandgap; a second semiconductor layer having a second, largerbandgap, said first and second semiconductor layers being stackedalternately, a material layer having a bandgap intermediate between saidfirst and second bandgaps, provided between said first and secondsemiconductor layer, said material layer changing a valence band energythereof in a thickness direction from said first semiconductor layer tosaid second semiconductor layer, said material layer comprising a firstlayer adjacent to said first semiconductor layer and a second layeradjacent to said second semiconductor layer, said first layer and secondlayer having first and second rates of compositional change such thatsaid first rate being larger than said second rate.
 43. An opticalinterconnection system, comprising: a surface-emission laser diode arraycomprising a substrate and a plurality of surface-emission laser diodesprovided commonly on said substrate; and an optical transmission pathcoupled optically to each of said plurality of surface-emission laserdiodes, each of said plurality of surface-emission laser diodescomprising: an active layer; and a resonator cooperating with saidactive layer, said active layer comprising upper and lower reflectorsdisposed above and below said active layer, at least one of said upperand lower reflectors comprising a distributed Bragg reflector,comprising: a first semiconductor layer having a first, largerrefractive index; a second semiconductor layer having a second, lowerrefractive index, said first and second semiconductor layers beingstacked alternately, a material layer having a refractive indexintermediate between said first and second refractive indices, saiddistributed Bragg reflector being tuned to a wavelength of 1.1 μm orlonger, wherein there is provided a material layer having a refractiveindex intermediate between said first refractive index and said secondrefractive index, said material layer having a thickness equal to orlarger than 5 nm but equal to or smaller than 50 nm.
 44. An opticalinterconnection system, comprising: a surface-emission laser diode arraycomprising a substrate and a plurality of surface-emission laser diodesformed commonly on said substrate; and an optical transmission pathcoupled optically to each of said plurality of surface-emission laserdiodes, each of said surface-emission laser diodes comprising: an activelayer; and a resonator cooperating with said active layer, said activelayer comprising upper and lower reflectors disposed above and belowsaid active layer, at least one of said upper and lower reflectorscomprising a distributed Bragg reflector, comprising: a firstsemiconductor layer having a first, larger refractive index; a secondsemiconductor layer having a second, lower refractive index, said firstand second semiconductor layers being stacked alternately, a materiallayer having a refractive index intermediate between said first andsecond refractive indices, said distributed Bragg reflector being tunedto a wavelength of 1.1 μm or longer, wherein there is provided amaterial layer having a refractive index intermediate between said firstrefractive index and said second refractive index, said material layerhaving a thickness smaller than (50λ−15) [nm] where λ is a tunedwavelength of the distributed Bragg reflector.
 45. An opticalinterconnection system, comprising: a surface-emission laser diode arraycomprising a plurality of surface-emission laser diodes; and an opticaltransmission path coupled optically to each of said plurality ofsurface-emission laser diodes, each of said surface-emission laserdiodes comprising: an active layer; and a resonator cooperating withsaid active layer, said active layer comprising upper and lowerreflectors disposed above and below said active layer, at least one ofsaid upper and lower reflectors comprising a distributed Braggreflector, comprising: a first semiconductor layer having a first,smaller bandgap; a second semiconductor layer having a second, largerbandgap, said first and second semiconductor layers being stackedalternately, a material layer having a bandgap intermediate between saidfirst and second bandgaps, provided between said first and secondsemiconductor layer, said material layer changing a valence band energythereof in a thickness direction from said first semiconductor layer tosaid second semiconductor layer, said material layer comprising a firstlayer adjacent to said first semiconductor layer and a second layeradjacent to said second semiconductor layer, said first layer and secondlayer having first and second rates of compositional change such thatsaid first rate being larger than said second rate.
 46. An opticaltelecommunication system, comprising: a surface-emission laser diode;and an optical transmission path coupled optically to saidsurface-emission laser diode, said surface-emission laser diodecomprising: an active layer; and a resonator cooperating with saidactive layer, said active layer comprising upper and lower reflectorsdisposed above and below said active layer, at least one of said upperand lower reflectors comprising a distributed Bragg reflector,comprising: a first semiconductor layer having a first, largerrefractive index; a second semiconductor layer having a second, lowerrefractive index, said first and second semiconductor layers beingstacked alternately, a material layer having a refractive indexintermediate between said first and second refractive indices, saiddistributed Bragg reflector being tuned to a wavelength of 1.1 μm orlonger, wherein there is provided a material layer having a refractiveindex intermediate between said first refractive index and said secondrefractive index, said material layer having a thickness equal to orlarger than 5 nm but equal to or smaller than 50 nm.
 47. An opticaltelecommunication system, comprising: a surface-emission laser diode;and an optical transmission path coupled optically to saidsurface-emission laser diode, said surface-emission laser diodecomprising: an active layer; and a resonator cooperating with saidactive layer, said active layer comprising upper and lower reflectorsdisposed above and below said active layer, at least one of said upperand lower reflectors comprising a distributed Bragg reflector,comprising: a first semiconductor layer having a first, largerrefractive index; a second semiconductor layer having a second, lowerrefractive index, said first and second semiconductor layers beingstacked alternately, a material layer having a refractive indexintermediate between said first and second refractive indices, saiddistributed Bragg reflector being tuned to a wavelength of 1.1 μm orlonger, wherein there is provided a material layer having a refractiveindex intermediate between said first refractive index and said secondrefractive index, said material layer having a thickness smaller than(50λ−15) [nm] where λ is a tuned wavelength of the distributed Braggreflector.
 48. An optical telecommunication system, comprising: asurface-emission laser diode; and an optical transmission path coupledoptically to said surface-emission laser diode, said surface-emissionlaser diode comprising: an active layer; and a resonator cooperatingwith said active layer, said active layer comprising upper and lowerreflectors disposed above and below said active layer, at least one ofsaid upper and lower reflectors comprising a distributed Braggreflector, comprising: a first semiconductor layer having a first,smaller bandgap; a second semiconductor layer having a second, largerbandgap, said first and second semiconductor layers being stackedalternately, a material layer having a bandgap intermediate between saidfirst and second bandgaps, provided between said first and secondsemiconductor layer, said material layer changing a valence band energythereof in a thickness direction from said first semiconductor layer tosaid second semiconductor layer, said material layer comprising a firstlayer adjacent to said first semiconductor layer and a second layeradjacent to said second semiconductor layer, said first layer and secondlayer having first and second rates of compositional change such thatsaid first rate being larger than said second rate.
 49. An opticaltelecommunication system, comprising: a surface-emission laser diodearray comprising a substrate and a plurality of surface-emission laserdiodes provided commonly on said substrate; and an optical transmissionpath coupled optically to each of said plurality of surface-emissionlaser diodes, each of said plurality of surface-emission laser diodescomprising: an active layer; and a resonator cooperating with saidactive layer, said active layer comprising upper and lower reflectorsdisposed above and below said active layer, at least one of said upperand lower reflectors comprising a distributed Bragg reflector,comprising: a first semiconductor layer having a first, largerrefractive index; a second semiconductor layer having a second, lowerrefractive index, said first and second semiconductor layers beingstacked alternately, a material layer having a refractive indexintermediate between said first and second refractive indices, saiddistributed Bragg reflector being tuned to a wavelength of 1.1 μm orlonger, wherein there is provided a material layer having a refractiveindex intermediate between said first refractive index and said secondrefractive index, said material layer having a thickness equal to orlarger than 5 nm but equal to or smaller than 50 nm.
 50. An opticaltelecommunication system, comprising: a surface-emission laser diodearray comprising a substrate and a plurality of surface-emission laserdiodes formed commonly on said substrate; and an optical transmissionpath coupled optically to each of said plurality of surface-emissionlaser diodes, each of said surface-emission laser diodes comprising: anactive layer; and a resonator cooperating with said active layer, saidactive layer comprising upper and lower reflectors disposed above andbelow said active layer, at least one of said upper and lower reflectorscomprising a distributed Bragg reflector, comprising: a firstsemiconductor layer having a first, larger refractive index; a secondsemiconductor layer having a second, lower refractive index, said firstand second semiconductor layers being stacked alternately, a materiallayer having a refractive index intermediate between said first andsecond refractive indices, said distributed Bragg reflector being tunedto a wavelength of 1.1 μm or longer, wherein there is provided amaterial layer having a refractive index intermediate between said firstrefractive index and said second refractive index, said material layerhaving a thickness smaller than (50λ−15) [nm] where λ is a tunedwavelength of the distributed Bragg reflector.
 51. An opticaltelecommunication system, comprising: a surface-emission laser diodearray comprising a plurality of surface-emission laser diodes; and anoptical transmission path coupled optically to each of said plurality ofsurface-emission laser diodes, each of said surface-emission laserdiodes comprising: an active layer; and a resonator cooperating withsaid active layer, said active layer comprising upper and lowerreflectors disposed above and below said active layer, at least one ofsaid upper and lower reflectors comprising a distributed Braggreflector, comprising: a first semiconductor layer having a first,smaller bandgap; a second semiconductor layer having a second, largerbandgap, said first and second semiconductor layers being stackedalternately, a material layer having a bandgap intermediate between saidfirst and second bandgaps, provided between said first and secondsemiconductor layer, said material layer changing a valence band energythereof in a thickness direction from said first semiconductor layer tosaid second semiconductor layer, said material layer comprising a firstlayer adjacent to said first semiconductor layer and a second layeradjacent to said second semiconductor layer, said first layer and secondlayer having first and second rates of compositional change such thatsaid first rate being larger than said second rate.
 52. An opticaltransmission/reception system, comprising: an optical source formed of asurface-emission Laser diode device, said surface-emission laser diodecomprising: an active layer of any of a layer containing Ga, In, N andAs as major constituent elements thereof and a layer containing Ga, Inand As as major constituent elements thereof, said active layerproducing optical radiation with a laser oscillation wavelength of1.1-1.7 μm; and a cavity structure comprising a pair of reflectorsprovided above and below said active layer, each of said reflectorsforming a semiconductor distributed Bragg reflector reflecting opticalradiation having a wavelength of 1.1 μm or more and comprising analternate and repetitive stacking of a first material layer ofAl_(x)Ga_(1-x)As (0<x≦1) and a second material layer of Al_(y)Ga_(1-y)As(0≦y<x≦1), wherein there is provided a hetero spike buffer layer betweensaid first material layer and said second material layer, said heterospike buffer layer having a refractive index intermediate between arefractive index of said first material layer and a refractive index ofsaid second material layer, said hetero spike buffer layer having acomposition represented as AlzGa1-zAs (0≦y<z<x≦1) and a thickness of20-50 nm; an optical fiber transmission path having an end coupledoptically to said optical source; and a photodetection unit coupled tothe other end of said optical fiber transmission path, said opticalfiber transmission path being bent between a point A, in which saidoptical source is provided, and a point B, in which said photodetectionunit is provided, such that there is no localized angle formed in saidoptical fiber transmission path.
 53. An optical transmission/receptionsystem, comprising: an optical source formed of a surface-emission laserdiode device, said surface-emission laser diode comprising: an activelayer of any of a layer containing Ga, In, N and As as major constituentelements thereof and a layer containing Ga, In and As as majorconstituent elements thereof, said active layer producing opticalradiation with a laser oscillation wavelength of 1.1-1.7 μm; and acavity structure comprising a pair of reflectors provided above andbelow said active layer, each of said reflectors forming a semiconductordistributed Bragg reflector reflecting optical radiation having awavelength of 1.1 μm or more and comprising an alternate and repetitivestacking of a first material layer of AixGa_(1-x)As (0<x≦1) and a secondmaterial layer of AlyGa_(1-y)As (0≦y<x≦1), wherein there is provided ahetero spike buffer layer between said first material layer and saidsecond material layer, said hetero spike buffer layer having arefractive index intermediate between a refractive index of said firstmaterial layer and a refractive index of said second material layer,said hetero spike buffer layer having a composition represented asAlzGa1-zAs (0≦y<z<x≦1) and a thickness of 20-50 nm; an optical fibertransmission path having an end coupled to said optical source; aphotodetection unit coupled to another end of said optical fibertransmission path; and a mirror provided between a point A, in whichsaid optical source is provided, and a point B, in which saidphotodetection unit is provided, said mirror changing a direction ofpropagation of an optical signal transmitted through said optical fibertransmission path.
 54. An optical transmission/reception system for usein an apparatus, comprising: an apparatus body; a surface-emission laserdiode device provided in said apparatus body as a laser optical source,said laser optical source producing an optical signal; a photodetectionunit provided in said apparatus body, said photodetection unit receivingsaid optical signal; a cover member covering a light emitting part ofsaid laser optical source; and another cover member covering aphotodetection part of said photodetection unit, said surface-emissionlaser diode comprising: an active layer of any of a layer containing Ga,In, N and As as major constituent elements thereof and a layercontaining Ga, In and As as major constituent elements thereof, saidactive layer producing optical radiation with a laser oscillationwavelength of 1.1-1.7 μm; and a cavity structure comprising a pair ofreflectors provided above and below said active layer, each of saidreflectors forming a semiconductor distributed Bragg reflectorreflecting optical radiation having a wavelength of 1.1 μm or more andcomprising an alternate and repetitive stacking of a first materiallayer of Al_(x)Ga_(1-x)As (0<x≦1) and a second material layer ofAl_(y)Ga_(1-y)As (0≦y<x≦1), wherein there is provided a hetero spikebuffer layer between said first material layer and said second materiallayer, said hetero spike buffer layer having a refractive indexintermediate between a refractive index of said first material layer anda refractive index of said second material layer, said hetero spikebuffer layer having a composition represented as AlzGa1-zAs (0≦y<z<x≦1)and a thickness of 20-50 nm.
 55. An optical telecommunication system,comprising: a laser diode; a first optical fiber coupled optically tosaid laser diode, said first optical fiber being injected with a laserbeam produced by said laser diode; a second optical fiber coupledoptically to said first optical fiber, said second optical fiber beinginjected with an optical signal transmitted through said first opticalfiber; a third optical fiber coupled optically to said second opticalfiber, said third optical fiber being injected with an optical signaltransmitted through said second optical fiber; and a photodetectorcoupled optically to said third optical fiber, said photodetectordetecting an optical signal transmitted through said third opticalfiber, said laser diode comprising a surface-emission laser diode chipand comprising: an active layer of any of a layer containing Ga, In, Nand As as major constituent elements thereof and a layer containing Ga,In and As as major constituent elements thereof, said active layerproducing optical radiation with a laser oscillation wavelength of1.1-1.7 μm; and a cavity structure comprising a pair of reflectorsprovided above and below said active layer, each of said reflectorsforming a semiconductor distributed Bragg reflector reflecting opticalradiation having a wavelength of 1.1 μm or more and comprising analternate and repetitive stacking of a first material layer ofAl_(x)Ga_(1-x)As (0<x≦1) and a second material layer of AlyGa_(1-y)As(0≦y<x≦1), wherein there is provided a hetero spike buffer layer betweensaid first material layer and said second material layer, said heterospike buffer layer having a refractive index intermediate between arefractive index of said first material layer and a refractive index ofsaid second material layer, said hetero spike buffer layer having acomposition represented as AlzGa1-zAs (0≦y<z<x≦1) and a thickness of20-50 nm.
 56. An optical telecommunication system, comprising: a laserdiode; a first optical fiber coupled optically to said laser diode, saidfirst optical fiber being injected with a laser beam produced by saidlaser diode; a second optical fiber coupled optically to said firstoptical fiber, said second optical fiber being injected with an opticalsignal transmitted through said first optical fiber; a third opticalfiber coupled optically to said second optical fiber, said third opticalfiber being injected with an optical signal transmitted through saidsecond optical fiber, said laser diode comprising a surface-emissionlaser diode chip and comprising: an active layer of any of a layercontaining Ga, In, N and As as major constituent elements thereof and alayer containing Ga, In and As as major constituent elements thereof,said active layer producing optical radiation with a laser oscillationwavelength of 1.1-1.7 μm; and a cavity structure comprising a pair ofreflectors provided above and below said active layer, each of saidreflectors forming a semiconductor distributed Bragg reflectorreflecting optical radiation having a wavelength of 1.1 μm or more andcomprising an alternate and repetitive stacking of a first materiallayer of Al_(x)Ga_(1-x)As (0<x≦1) and a second material layer ofAl_(y)Ga_(1-y)As (0≦y<x≦1), wherein there is provided a hetero spikebuffer layer between said first material layer and said second materiallayer, said hetero spike buffer layer having a refractive indexintermediate between a refractive index of said first material layer anda refractive index of said second material layer, said hetero spikebuffer layer having a composition represented as AlzGa_(1-z)As(0-≦y<z<x≦1) and a thickness of 20-50 nm, said first optical fiberhaving a length of 1 mm or more.
 57. An optical telecommunication systemcomprising: a laser diode; and an optical transmission path coupledoptically to said laser diode, said laser diode comprising asurface-emission laser diode chip and comprising: an active layer of anyof a layer containing Ga, in, N and As as major constituent elementsthereof and a layer containing Ga, In and As as major constituentelements thereof, said active layer producing optical radiation with alaser oscillation wavelength of 1.1-1.7 μm; and a cavity structurecomprising a pair of reflectors provided above and below said activelayer, each of said reflectors forming a semiconductor distributed Braggreflector reflecting optical radiation having a wavelength of 1.1 μm ormore and comprising an alternate and repetitive stacking of a firstmaterial layer of Al_(x)Ga_(1-x)As (0<x≦1) and a second material layerof Al_(y)Ga_(1-y)As (0≦y<x≦1), wherein there is provided a hetero spikebuffer layer between said first material layer and said second materiallayer, said hetero spike buffer layer having a refractive indexintermediate between a refractive index of said first material layer anda refractive index of said second material layer, said hetero spikebuffer layer having a composition represented as AlzGa1-zAs (0≦y<z<x≦1)and a thickness of 20-50 nm, said optical transmission path comprisingan optical fiber having a length L, said optical fiber including a corehaving a diamter D and a clad, wherein there holds a relationship 10⁵≦L/D≦10⁹.
 58. An optical telecommunication system, comprising: a laserdiode, a mount substrate on which said laser diode is mounted; saidlaser diode comprising a surface-emission laser diode chip andcomprising: an active layer of any of a layer containing Ga, In, N andAs as major constituent elements thereof and a layer containing Ga, Inand As as major constituent elements thereof, said active layerproducing optical radiation with a laser oscillation wavelength of 1.1-1.7 μm; and a cavity structure comprising a pair of reflectors providedabove and below said active layer, each of said reflectors forming asemiconductor distributed Bragg reflector reflecting optical radiationhaving a wavelength of 1.1/m or more and-comprising an alternate andrepetitive stacking of a first material layer of AlxGa_(1-x)As (0<x≦1)and a second material layer of AlyGa_(1-y)As (0y≦x≦1), wherein there isprovided a hetero spike buffer layer between said first material layerand said second material layer, said hetero spike buffer layer having arefractive index intermediate between a refractive index of said firstmaterial layer and a refractive index of said second material layer,said hetero spike buffer layer having a composition represented asAlzGa_(1-z)As (0≦y<z>1) and a thickness of 20-50 nm, wherein adifference of linear thermal expansion coefficient between said laserdiode and said substrate is within 2×10⁻⁶/K.
 59. An opticaltelecommunication system, comprising: a laser diode; and an opticalfiber coupled optically to said laser diode, said laser diode comprisinga surface-emission laser diode chip and comprising: an active layer ofany of a layer containing Ga, In, N and As as major constituent elementsthereof and a layer containing Ga, In and As as major constituentelements thereof, said active layer producing optical radiation with alaser oscillation wavelength of 1.1-1.7 μm; and a cavity structurecomprising a pair of reflectors provided above and below said activelayer, each of said reflectors forming a semiconductor distributed Braggreflector reflecting optical radiation having a wavelength of 1.1 μm ormore and comprising an alternate and repetitive stacking of a firstmaterial layer of Al_(x)Ga_(1-x)As (0<x≦1) and a second material layerof Al_(y)Ga_(1-y)As (0≦y<x≦1), wherein there is provided a hetero spikebuffer layer between said first material layer and said second materiallayer, said hetero spike buffer layer having a refractive indexintermediate between a refractive index of said first material layer anda refractive index of said second material layer, said hetero spikebuffer layer having a composition represented as AlzGa1-zAs (0≦y<z<x≦1)and a is thickness of 20-50 nm, wherein said optical fiber ismechanically connected to said laser diode in the state that saidoptical fiber is urged in an axial direction thereof toward a lightemitting part of said laser diode.
 60. An optical telecommunicationsystem, comprising: a laser diode; and one of an optical fiber and anoptical waveguide coupled optically to said laser diode, said laserdiode comprising a surface-emission laser diode chip and comprising: anactive layer of any of a layer containing Ga, In, N and As as majorconstituent elements thereof and a layer containing Ga, In and As asmajor constituent elements thereof, said active layer producing opticalradiation with a laser oscillation wavelength of 1.1-1.7 μm; and acavity structure comprising a pair of reflectors provided above andbelow said active layer, each of said reflectors forming a semiconductordistributed Bragg reflector reflecting optical radiation having awavelength of 1.1 μm or more and comprising an alternate and repetitivestacking of a first material layer of Al_(x)Ga_(1-x)As (0<x≦1) and asecond material layer of Al_(y)Ga_(1-y)As (0≦y<x≦1), wherein there isprovided a hetero spike buffer layer between said first material layerand said second material layer, said hetero spike buffer layer having arefractive index intermediate between a refractive index of said firstmaterial layer and a refractive index of said second material layer,said hetero spike buffer layer having a composition represented asAlzGa1-zAs (0≦y<z<x≦1) and a thickness of 20-50 nm, said optical fiberor said optical waveguide having a core with a diameter X, said laserdiode having an aperture d and an optical emission angle θ, whereinthere holds a relationship d+2ltan(θ/2)≦X, where l represents an opticalpath length from said laser diode to an edge of said optical fiber oroptical waveguide.
 61. An optical telecommunication system, comprising:a laser diode; and an optical waveguide coupled optically to said laserdiode, said laser diode comprising a surface-emission laser diode chipand comprising: an active layer of any of a layer containing Ga, In, Nand As as major constituent elements thereof and a layer containing Ga,In and As as major constituent elements thereof, said active layerproducing optical radiation with a laser oscillation wavelength of1.1-1.7 μm; and a cavity structure comprising a pair of reflectorsprovided above and below said active layer, each of said reflectorsforming a semiconductor distributed Bragg reflector reflecting opticalradiation having a wavelength of 1.1 μm or more and comprising analternate and repetitive stacking of a first material layer ofAl_(x)Ga_(1-x)As (0<x≦1) and a second material layer of Al_(y)Ga_(1-y)As(0≦y<x≦1), wherein there is provided a hetero spike buffer layer betweensaid first material layer and said second material layer, said heterospike buffer layer having a refractive index intermediate between arefractive index of said first material layer and a refractive index ofsaid second material layer, said hetero spike buffer layer having acomposition represented as AlzGa1-zAs (0≦y<z<x≦1) and a thickness of20-50 nm, wherein there holds a relationship 0.5≦F/d≦2 where drepresents a diameter of a circle touching internally to an opticalemission part of said laser diode and F represents a core diameter ofsaid optical fiber.
 62. An optical telecommunication system, comprising:a laser diode; and an optical waveguide coupled optically to a laserchip, said laser diode comprising a surface-emission laser-diode chipand comprising: an active layer of any of a layer containing Ga, In, Nand As as major constituent elements thereof and a layer containing Ga,In and As as major constituent elements thereof, said active layerproducing optical radiation with a laser oscillation wavelength of1.1-1.7 μm; and a cavity structure comprising a pair of reflectorsprovided above and below said active layer, each of said reflectorsforming a semiconductor distributed Bragg reflector reflecting opticalradiation having a wavelength of 1.1 μm or more and comprising analternate and repetitive stacking of a first material layer ofAl_(x)Ga_(1-x)As (0<x≦1) and a second material layer of Al_(y)Ga_(1-y)As(0≦y<x≦1), wherein there is provided a hetero spike buffer layer betweensaid first material layer and said second material layer, said heterospike buffer layer having a refractive index intermediate between arefractive index of said first material layer and a refractive index ofsaid second material layer, said hetero spike buffer layer having acomposition represented as AlzGa1-zAs (0≦y<z<x≦1) and a thickness of20-50 nm, said laser diode including an optical emission part having anarea S [mm²], said laser diode being driven with an operational voltageV [volts], wherein a parameter V/S falls in a range from 15000 to 30000.